Fix stale sub-cursor C_INIT flag

[openldap] / libraries / liblmdb / mdb.c

/** @file mdb.c
 *      @brief memory-mapped database library
 *
 *      A Btree-based database management library modeled loosely on the
 *      BerkeleyDB API, but much simplified.
 */
/*
 * Copyright 2011-2013 Howard Chu, Symas Corp.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted only as authorized by the OpenLDAP
 * Public License.
 *
 * A copy of this license is available in the file LICENSE in the
 * top-level directory of the distribution or, alternatively, at
 * <http://www.OpenLDAP.org/license.html>.
 *
 * This code is derived from btree.c written by Martin Hedenfalk.
 *
 * Copyright (c) 2009, 2010 Martin Hedenfalk <martin@bzero.se>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */
#ifndef _GNU_SOURCE
#define _GNU_SOURCE 1
#endif
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/param.h>
#ifdef _WIN32
#include <windows.h>
#else
#include <sys/uio.h>
#include <sys/mman.h>
#ifdef HAVE_SYS_FILE_H
#include <sys/file.h>
#endif
#include <fcntl.h>
#endif

#include <assert.h>
#include <errno.h>
#include <limits.h>
#include <stddef.h>
#include <inttypes.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>

#if !(defined(BYTE_ORDER) || defined(__BYTE_ORDER))
#include <netinet/in.h>
#include <resolv.h>     /* defines BYTE_ORDER on HPUX and Solaris */
#endif

#if defined(__APPLE__) || defined (BSD)
# define MDB_USE_POSIX_SEM      1
# define MDB_FDATASYNC          fsync
#elif defined(ANDROID)
# define MDB_FDATASYNC          fsync
#endif

#ifndef _WIN32
#include <pthread.h>
#ifdef MDB_USE_POSIX_SEM
#include <semaphore.h>
#endif
#endif

#ifdef USE_VALGRIND
#include <valgrind/memcheck.h>
#define VGMEMP_CREATE(h,r,z)    VALGRIND_CREATE_MEMPOOL(h,r,z)
#define VGMEMP_ALLOC(h,a,s) VALGRIND_MEMPOOL_ALLOC(h,a,s)
#define VGMEMP_FREE(h,a) VALGRIND_MEMPOOL_FREE(h,a)
#define VGMEMP_DESTROY(h)       VALGRIND_DESTROY_MEMPOOL(h)
#define VGMEMP_DEFINED(a,s)     VALGRIND_MAKE_MEM_DEFINED(a,s)
#else
#define VGMEMP_CREATE(h,r,z)
#define VGMEMP_ALLOC(h,a,s)
#define VGMEMP_FREE(h,a)
#define VGMEMP_DESTROY(h)
#define VGMEMP_DEFINED(a,s)
#endif

#ifndef BYTE_ORDER
# if (defined(_LITTLE_ENDIAN) || defined(_BIG_ENDIAN)) && !(defined(_LITTLE_ENDIAN) && defined(_BIG_ENDIAN))
/* Solaris just defines one or the other */
#  define LITTLE_ENDIAN 1234
#  define BIG_ENDIAN    4321
#  ifdef _LITTLE_ENDIAN
#   define BYTE_ORDER  LITTLE_ENDIAN
#  else
#   define BYTE_ORDER  BIG_ENDIAN
#  endif
# else
#  define BYTE_ORDER   __BYTE_ORDER
# endif
#endif

#ifndef LITTLE_ENDIAN
#define LITTLE_ENDIAN   __LITTLE_ENDIAN
#endif
#ifndef BIG_ENDIAN
#define BIG_ENDIAN      __BIG_ENDIAN
#endif

#if defined(__i386) || defined(__x86_64) || defined(_M_IX86)
#define MISALIGNED_OK   1
#endif

#include "lmdb.h"
#include "midl.h"

#if (BYTE_ORDER == LITTLE_ENDIAN) == (BYTE_ORDER == BIG_ENDIAN)
# error "Unknown or unsupported endianness (BYTE_ORDER)"
#elif (-6 & 5) || CHAR_BIT != 8 || UINT_MAX < 0xffffffff || ULONG_MAX % 0xFFFF
# error "Two's complement, reasonably sized integer types, please"
#endif

/** @defgroup internal  MDB Internals
 *      @{
 */
/** @defgroup compat    Windows Compatibility Macros
 *      A bunch of macros to minimize the amount of platform-specific ifdefs
 *      needed throughout the rest of the code. When the features this library
 *      needs are similar enough to POSIX to be hidden in a one-or-two line
 *      replacement, this macro approach is used.
 *      @{
 */
#ifdef _WIN32
#define pthread_t       DWORD
#define pthread_mutex_t HANDLE
#define pthread_key_t   DWORD
#define pthread_self()  GetCurrentThreadId()
#define pthread_key_create(x,y) \
        ((*(x) = TlsAlloc()) == TLS_OUT_OF_INDEXES ? ErrCode() : 0)
#define pthread_key_delete(x)   TlsFree(x)
#define pthread_getspecific(x)  TlsGetValue(x)
#define pthread_setspecific(x,y)        (TlsSetValue(x,y) ? 0 : ErrCode())
#define pthread_mutex_unlock(x) ReleaseMutex(x)
#define pthread_mutex_lock(x)   WaitForSingleObject(x, INFINITE)
#define LOCK_MUTEX_R(env)       pthread_mutex_lock((env)->me_rmutex)
#define UNLOCK_MUTEX_R(env)     pthread_mutex_unlock((env)->me_rmutex)
#define LOCK_MUTEX_W(env)       pthread_mutex_lock((env)->me_wmutex)
#define UNLOCK_MUTEX_W(env)     pthread_mutex_unlock((env)->me_wmutex)
#define getpid()        GetCurrentProcessId()
#define MDB_FDATASYNC(fd)       (!FlushFileBuffers(fd))
#define MDB_MSYNC(addr,len,flags)       (!FlushViewOfFile(addr,len))
#define ErrCode()       GetLastError()
#define GET_PAGESIZE(x) {SYSTEM_INFO si; GetSystemInfo(&si); (x) = si.dwPageSize;}
#define close(fd)       (CloseHandle(fd) ? 0 : -1)
#define munmap(ptr,len) UnmapViewOfFile(ptr)
#else

#ifdef MDB_USE_POSIX_SEM

#define LOCK_MUTEX_R(env)       mdb_sem_wait((env)->me_rmutex)
#define UNLOCK_MUTEX_R(env)     sem_post((env)->me_rmutex)
#define LOCK_MUTEX_W(env)       mdb_sem_wait((env)->me_wmutex)
#define UNLOCK_MUTEX_W(env)     sem_post((env)->me_wmutex)

static int
mdb_sem_wait(sem_t *sem)
{
   int rc;
   while ((rc = sem_wait(sem)) && (rc = errno) == EINTR) ;
   return rc;
}

#else
        /** Lock the reader mutex.
         */
#define LOCK_MUTEX_R(env)       pthread_mutex_lock(&(env)->me_txns->mti_mutex)
        /** Unlock the reader mutex.
         */
#define UNLOCK_MUTEX_R(env)     pthread_mutex_unlock(&(env)->me_txns->mti_mutex)

        /** Lock the writer mutex.
         *      Only a single write transaction is allowed at a time. Other writers
         *      will block waiting for this mutex.
         */
#define LOCK_MUTEX_W(env)       pthread_mutex_lock(&(env)->me_txns->mti_wmutex)
        /** Unlock the writer mutex.
         */
#define UNLOCK_MUTEX_W(env)     pthread_mutex_unlock(&(env)->me_txns->mti_wmutex)
#endif  /* MDB_USE_POSIX_SEM */

        /** Get the error code for the last failed system function.
         */
#define ErrCode()       errno

        /** An abstraction for a file handle.
         *      On POSIX systems file handles are small integers. On Windows
         *      they're opaque pointers.
         */
#define HANDLE  int

        /**     A value for an invalid file handle.
         *      Mainly used to initialize file variables and signify that they are
         *      unused.
         */
#define INVALID_HANDLE_VALUE    (-1)

        /** Get the size of a memory page for the system.
         *      This is the basic size that the platform's memory manager uses, and is
         *      fundamental to the use of memory-mapped files.
         */
#define GET_PAGESIZE(x) ((x) = sysconf(_SC_PAGE_SIZE))
#endif

#if defined(_WIN32) || defined(MDB_USE_POSIX_SEM)
#define MNAME_LEN       32
#else
#define MNAME_LEN       (sizeof(pthread_mutex_t))
#endif

/** @} */

#ifndef _WIN32
/**     A flag for opening a file and requesting synchronous data writes.
 *      This is only used when writing a meta page. It's not strictly needed;
 *      we could just do a normal write and then immediately perform a flush.
 *      But if this flag is available it saves us an extra system call.
 *
 *      @note If O_DSYNC is undefined but exists in /usr/include,
 * preferably set some compiler flag to get the definition.
 * Otherwise compile with the less efficient -DMDB_DSYNC=O_SYNC.
 */
#ifndef MDB_DSYNC
# define MDB_DSYNC      O_DSYNC
#endif
#endif

/** Function for flushing the data of a file. Define this to fsync
 *      if fdatasync() is not supported.
 */
#ifndef MDB_FDATASYNC
# define MDB_FDATASYNC  fdatasync
#endif

#ifndef MDB_MSYNC
# define MDB_MSYNC(addr,len,flags)      msync(addr,len,flags)
#endif

#ifndef MS_SYNC
#define MS_SYNC 1
#endif

#ifndef MS_ASYNC
#define MS_ASYNC        0
#endif

        /** A page number in the database.
         *      Note that 64 bit page numbers are overkill, since pages themselves
         *      already represent 12-13 bits of addressable memory, and the OS will
         *      always limit applications to a maximum of 63 bits of address space.
         *
         *      @note In the #MDB_node structure, we only store 48 bits of this value,
         *      which thus limits us to only 60 bits of addressable data.
         */
typedef MDB_ID  pgno_t;

        /** A transaction ID.
         *      See struct MDB_txn.mt_txnid for details.
         */
typedef MDB_ID  txnid_t;

/** @defgroup debug     Debug Macros
 *      @{
 */
#ifndef MDB_DEBUG
        /**     Enable debug output.
         *      Set this to 1 for copious tracing. Set to 2 to add dumps of all IDLs
         *      read from and written to the database (used for free space management).
         */
#define MDB_DEBUG 0
#endif

#if !(__STDC_VERSION__ >= 199901L || defined(__GNUC__))
# undef  MDB_DEBUG
# define MDB_DEBUG      0
# define DPRINTF        (void)  /* Vararg macros may be unsupported */
#elif MDB_DEBUG
static int mdb_debug;
static txnid_t mdb_debug_start;

        /**     Print a debug message with printf formatting. */
# define DPRINTF(fmt, ...)      /**< Requires 2 or more args */ \
        ((void) ((mdb_debug) && \
         fprintf(stderr, "%s:%d " fmt "\n", __func__, __LINE__, __VA_ARGS__)))
#else
# define DPRINTF(fmt, ...)      ((void) 0)
# define MDB_DEBUG_SKIP
#endif
        /**     Print a debug string.
         *      The string is printed literally, with no format processing.
         */
#define DPUTS(arg)      DPRINTF("%s", arg)
/** @} */

        /** A default memory page size.
         *      The actual size is platform-dependent, but we use this for
         *      boot-strapping. We probably should not be using this any more.
         *      The #GET_PAGESIZE() macro is used to get the actual size.
         *
         *      Note that we don't currently support Huge pages. On Linux,
         *      regular data files cannot use Huge pages, and in general
         *      Huge pages aren't actually pageable. We rely on the OS
         *      demand-pager to read our data and page it out when memory
         *      pressure from other processes is high. So until OSs have
         *      actual paging support for Huge pages, they're not viable.
         */
#define MDB_PAGESIZE     4096

        /** The minimum number of keys required in a database page.
         *      Setting this to a larger value will place a smaller bound on the
         *      maximum size of a data item. Data items larger than this size will
         *      be pushed into overflow pages instead of being stored directly in
         *      the B-tree node. This value used to default to 4. With a page size
         *      of 4096 bytes that meant that any item larger than 1024 bytes would
         *      go into an overflow page. That also meant that on average 2-3KB of
         *      each overflow page was wasted space. The value cannot be lower than
         *      2 because then there would no longer be a tree structure. With this
         *      value, items larger than 2KB will go into overflow pages, and on
         *      average only 1KB will be wasted.
         */
#define MDB_MINKEYS      2

        /**     A stamp that identifies a file as an MDB file.
         *      There's nothing special about this value other than that it is easily
         *      recognizable, and it will reflect any byte order mismatches.
         */
#define MDB_MAGIC        0xBEEFC0DE

        /**     The version number for a database's file format. */
#define MDB_VERSION      1

        /**     @brief The maximum size of a key in the database.
         *
         *      The library rejects bigger keys, and cannot deal with records
         *      with bigger keys stored by a library with bigger max keysize.
         *
         *      We require that keys all fit onto a regular page. This limit
         *      could be raised a bit further if needed; to something just
         *      under #MDB_PAGESIZE / #MDB_MINKEYS.
         *
         *      Note that data items in an #MDB_DUPSORT database are actually keys
         *      of a subDB, so they're also limited to this size.
         */
#ifndef MDB_MAXKEYSIZE
#define MDB_MAXKEYSIZE   511
#endif

        /**     @brief The maximum size of a data item.
         *
         *      We only store a 32 bit value for node sizes.
         */
#define MAXDATASIZE     0xffffffffUL

#if MDB_DEBUG
        /**     A key buffer.
         *      @ingroup debug
         *      This is used for printing a hex dump of a key's contents.
         */
#define DKBUF   char kbuf[(MDB_MAXKEYSIZE*2+1)]
        /**     Display a key in hex.
         *      @ingroup debug
         *      Invoke a function to display a key in hex.
         */
#define DKEY(x) mdb_dkey(x, kbuf)
#else
#define DKBUF   typedef int dummy_kbuf  /* so we can put ';' after */
#define DKEY(x) 0
#endif

        /** An invalid page number.
         *      Mainly used to denote an empty tree.
         */
#define P_INVALID        (~(pgno_t)0)

        /** Test if the flags \b f are set in a flag word \b w. */
#define F_ISSET(w, f)    (((w) & (f)) == (f))

        /**     Used for offsets within a single page.
         *      Since memory pages are typically 4 or 8KB in size, 12-13 bits,
         *      this is plenty.
         */
typedef uint16_t         indx_t;

        /**     Default size of memory map.
         *      This is certainly too small for any actual applications. Apps should always set
         *      the size explicitly using #mdb_env_set_mapsize().
         */
#define DEFAULT_MAPSIZE 1048576

/**     @defgroup readers       Reader Lock Table
 *      Readers don't acquire any locks for their data access. Instead, they
 *      simply record their transaction ID in the reader table. The reader
 *      mutex is needed just to find an empty slot in the reader table. The
 *      slot's address is saved in thread-specific data so that subsequent read
 *      transactions started by the same thread need no further locking to proceed.
 *
 *      If #MDB_NOTLS is set, the slot address is not saved in thread-specific data.
 *
 *      No reader table is used if the database is on a read-only filesystem.
 *
 *      Since the database uses multi-version concurrency control, readers don't
 *      actually need any locking. This table is used to keep track of which
 *      readers are using data from which old transactions, so that we'll know
 *      when a particular old transaction is no longer in use. Old transactions
 *      that have discarded any data pages can then have those pages reclaimed
 *      for use by a later write transaction.
 *
 *      The lock table is constructed such that reader slots are aligned with the
 *      processor's cache line size. Any slot is only ever used by one thread.
 *      This alignment guarantees that there will be no contention or cache
 *      thrashing as threads update their own slot info, and also eliminates
 *      any need for locking when accessing a slot.
 *
 *      A writer thread will scan every slot in the table to determine the oldest
 *      outstanding reader transaction. Any freed pages older than this will be
 *      reclaimed by the writer. The writer doesn't use any locks when scanning
 *      this table. This means that there's no guarantee that the writer will
 *      see the most up-to-date reader info, but that's not required for correct
 *      operation - all we need is to know the upper bound on the oldest reader,
 *      we don't care at all about the newest reader. So the only consequence of
 *      reading stale information here is that old pages might hang around a
 *      while longer before being reclaimed. That's actually good anyway, because
 *      the longer we delay reclaiming old pages, the more likely it is that a
 *      string of contiguous pages can be found after coalescing old pages from
 *      many old transactions together.
 *      @{
 */
        /**     Number of slots in the reader table.
         *      This value was chosen somewhat arbitrarily. 126 readers plus a
         *      couple mutexes fit exactly into 8KB on my development machine.
         *      Applications should set the table size using #mdb_env_set_maxreaders().
         */
#define DEFAULT_READERS 126

        /**     The size of a CPU cache line in bytes. We want our lock structures
         *      aligned to this size to avoid false cache line sharing in the
         *      lock table.
         *      This value works for most CPUs. For Itanium this should be 128.
         */
#ifndef CACHELINE
#define CACHELINE       64
#endif

        /**     The information we store in a single slot of the reader table.
         *      In addition to a transaction ID, we also record the process and
         *      thread ID that owns a slot, so that we can detect stale information,
         *      e.g. threads or processes that went away without cleaning up.
         *      @note We currently don't check for stale records. We simply re-init
         *      the table when we know that we're the only process opening the
         *      lock file.
         */
typedef struct MDB_rxbody {
        /**     Current Transaction ID when this transaction began, or (txnid_t)-1.
         *      Multiple readers that start at the same time will probably have the
         *      same ID here. Again, it's not important to exclude them from
         *      anything; all we need to know is which version of the DB they
         *      started from so we can avoid overwriting any data used in that
         *      particular version.
         */
        txnid_t         mrb_txnid;
        /** The process ID of the process owning this reader txn. */
        pid_t           mrb_pid;
        /** The thread ID of the thread owning this txn. */
        pthread_t       mrb_tid;
} MDB_rxbody;

        /** The actual reader record, with cacheline padding. */
typedef struct MDB_reader {
        union {
                MDB_rxbody mrx;
                /** shorthand for mrb_txnid */
#define mr_txnid        mru.mrx.mrb_txnid
#define mr_pid  mru.mrx.mrb_pid
#define mr_tid  mru.mrx.mrb_tid
                /** cache line alignment */
                char pad[(sizeof(MDB_rxbody)+CACHELINE-1) & ~(CACHELINE-1)];
        } mru;
} MDB_reader;

        /** The header for the reader table.
         *      The table resides in a memory-mapped file. (This is a different file
         *      than is used for the main database.)
         *
         *      For POSIX the actual mutexes reside in the shared memory of this
         *      mapped file. On Windows, mutexes are named objects allocated by the
         *      kernel; we store the mutex names in this mapped file so that other
         *      processes can grab them. This same approach is also used on
         *      MacOSX/Darwin (using named semaphores) since MacOSX doesn't support
         *      process-shared POSIX mutexes. For these cases where a named object
         *      is used, the object name is derived from a 64 bit FNV hash of the
         *      environment pathname. As such, naming collisions are extremely
         *      unlikely. If a collision occurs, the results are unpredictable.
         */
typedef struct MDB_txbody {
                /** Stamp identifying this as an MDB file. It must be set
                 *      to #MDB_MAGIC. */
        uint32_t        mtb_magic;
                /** Version number of this lock file. Must be set to #MDB_VERSION. */
        uint32_t        mtb_version;
#if defined(_WIN32) || defined(MDB_USE_POSIX_SEM)
        char    mtb_rmname[MNAME_LEN];
#else
                /** Mutex protecting access to this table.
                 *      This is the reader lock that #LOCK_MUTEX_R acquires.
                 */
        pthread_mutex_t mtb_mutex;
#endif
                /**     The ID of the last transaction committed to the database.
                 *      This is recorded here only for convenience; the value can always
                 *      be determined by reading the main database meta pages.
                 */
        txnid_t         mtb_txnid;
                /** The number of slots that have been used in the reader table.
                 *      This always records the maximum count, it is not decremented
                 *      when readers release their slots.
                 */
        unsigned        mtb_numreaders;
} MDB_txbody;

        /** The actual reader table definition. */
typedef struct MDB_txninfo {
        union {
                MDB_txbody mtb;
#define mti_magic       mt1.mtb.mtb_magic
#define mti_version     mt1.mtb.mtb_version
#define mti_mutex       mt1.mtb.mtb_mutex
#define mti_rmname      mt1.mtb.mtb_rmname
#define mti_txnid       mt1.mtb.mtb_txnid
#define mti_numreaders  mt1.mtb.mtb_numreaders
                char pad[(sizeof(MDB_txbody)+CACHELINE-1) & ~(CACHELINE-1)];
        } mt1;
        union {
#if defined(_WIN32) || defined(MDB_USE_POSIX_SEM)
                char mt2_wmname[MNAME_LEN];
#define mti_wmname      mt2.mt2_wmname
#else
                pthread_mutex_t mt2_wmutex;
#define mti_wmutex      mt2.mt2_wmutex
#endif
                char pad[(MNAME_LEN+CACHELINE-1) & ~(CACHELINE-1)];
        } mt2;
        MDB_reader      mti_readers[1];
} MDB_txninfo;
/** @} */

/** Common header for all page types.
 * Overflow records occupy a number of contiguous pages with no
 * headers on any page after the first.
 */
typedef struct MDB_page {
#define mp_pgno mp_p.p_pgno
#define mp_next mp_p.p_next
        union {
                pgno_t          p_pgno; /**< page number */
                void *          p_next; /**< for in-memory list of freed structs */
        } mp_p;
        uint16_t        mp_pad;
/**     @defgroup mdb_page      Page Flags
 *      @ingroup internal
 *      Flags for the page headers.
 *      @{
 */
#define P_BRANCH         0x01           /**< branch page */
#define P_LEAF           0x02           /**< leaf page */
#define P_OVERFLOW       0x04           /**< overflow page */
#define P_META           0x08           /**< meta page */
#define P_DIRTY          0x10           /**< dirty page */
#define P_LEAF2          0x20           /**< for #MDB_DUPFIXED records */
#define P_SUBP           0x40           /**< for #MDB_DUPSORT sub-pages */
#define P_KEEP           0x8000         /**< leave this page alone during spill */
/** @} */
        uint16_t        mp_flags;               /**< @ref mdb_page */
#define mp_lower        mp_pb.pb.pb_lower
#define mp_upper        mp_pb.pb.pb_upper
#define mp_pages        mp_pb.pb_pages
        union {
                struct {
                        indx_t          pb_lower;               /**< lower bound of free space */
                        indx_t          pb_upper;               /**< upper bound of free space */
                } pb;
                uint32_t        pb_pages;       /**< number of overflow pages */
        } mp_pb;
        indx_t          mp_ptrs[1];             /**< dynamic size */
} MDB_page;

        /** Size of the page header, excluding dynamic data at the end */
#define PAGEHDRSZ        ((unsigned) offsetof(MDB_page, mp_ptrs))

        /** Address of first usable data byte in a page, after the header */
#define METADATA(p)      ((void *)((char *)(p) + PAGEHDRSZ))

        /** Number of nodes on a page */
#define NUMKEYS(p)       (((p)->mp_lower - PAGEHDRSZ) >> 1)

        /** The amount of space remaining in the page */
#define SIZELEFT(p)      (indx_t)((p)->mp_upper - (p)->mp_lower)

        /** The percentage of space used in the page, in tenths of a percent. */
#define PAGEFILL(env, p) (1000L * ((env)->me_psize - PAGEHDRSZ - SIZELEFT(p)) / \
                                ((env)->me_psize - PAGEHDRSZ))
        /** The minimum page fill factor, in tenths of a percent.
         *      Pages emptier than this are candidates for merging.
         */
#define FILL_THRESHOLD   250

        /** Test if a page is a leaf page */
#define IS_LEAF(p)       F_ISSET((p)->mp_flags, P_LEAF)
        /** Test if a page is a LEAF2 page */
#define IS_LEAF2(p)      F_ISSET((p)->mp_flags, P_LEAF2)
        /** Test if a page is a branch page */
#define IS_BRANCH(p)     F_ISSET((p)->mp_flags, P_BRANCH)
        /** Test if a page is an overflow page */
#define IS_OVERFLOW(p)   F_ISSET((p)->mp_flags, P_OVERFLOW)
        /** Test if a page is a sub page */
#define IS_SUBP(p)       F_ISSET((p)->mp_flags, P_SUBP)

        /** The number of overflow pages needed to store the given size. */
#define OVPAGES(size, psize)    ((PAGEHDRSZ-1 + (size)) / (psize) + 1)

        /** Header for a single key/data pair within a page.
         * We guarantee 2-byte alignment for nodes.
         */
typedef struct MDB_node {
        /** lo and hi are used for data size on leaf nodes and for
         * child pgno on branch nodes. On 64 bit platforms, flags
         * is also used for pgno. (Branch nodes have no flags).
         * They are in host byte order in case that lets some
         * accesses be optimized into a 32-bit word access.
         */
#define mn_lo mn_offset[BYTE_ORDER!=LITTLE_ENDIAN]
#define mn_hi mn_offset[BYTE_ORDER==LITTLE_ENDIAN] /**< part of dsize or pgno */
        unsigned short  mn_offset[2];   /**< storage for #mn_lo and #mn_hi */
/** @defgroup mdb_node Node Flags
 *      @ingroup internal
 *      Flags for node headers.
 *      @{
 */
#define F_BIGDATA        0x01                   /**< data put on overflow page */
#define F_SUBDATA        0x02                   /**< data is a sub-database */
#define F_DUPDATA        0x04                   /**< data has duplicates */

/** valid flags for #mdb_node_add() */
#define NODE_ADD_FLAGS  (F_DUPDATA|F_SUBDATA|MDB_RESERVE|MDB_APPEND)

/** @} */
        unsigned short  mn_flags;               /**< @ref mdb_node */
        unsigned short  mn_ksize;               /**< key size */
        char            mn_data[1];                     /**< key and data are appended here */
} MDB_node;

        /** Size of the node header, excluding dynamic data at the end */
#define NODESIZE         offsetof(MDB_node, mn_data)

        /** Bit position of top word in page number, for shifting mn_flags */
#define PGNO_TOPWORD ((pgno_t)-1 > 0xffffffffu ? 32 : 0)

        /** Size of a node in a branch page with a given key.
         *      This is just the node header plus the key, there is no data.
         */
#define INDXSIZE(k)      (NODESIZE + ((k) == NULL ? 0 : (k)->mv_size))

        /** Size of a node in a leaf page with a given key and data.
         *      This is node header plus key plus data size.
         */
#define LEAFSIZE(k, d)   (NODESIZE + (k)->mv_size + (d)->mv_size)

        /** Address of node \b i in page \b p */
#define NODEPTR(p, i)    ((MDB_node *)((char *)(p) + (p)->mp_ptrs[i]))

        /** Address of the key for the node */
#define NODEKEY(node)    (void *)((node)->mn_data)

        /** Address of the data for a node */
#define NODEDATA(node)   (void *)((char *)(node)->mn_data + (node)->mn_ksize)

        /** Get the page number pointed to by a branch node */
#define NODEPGNO(node) \
        ((node)->mn_lo | ((pgno_t) (node)->mn_hi << 16) | \
         (PGNO_TOPWORD ? ((pgno_t) (node)->mn_flags << PGNO_TOPWORD) : 0))
        /** Set the page number in a branch node */
#define SETPGNO(node,pgno)      do { \
        (node)->mn_lo = (pgno) & 0xffff; (node)->mn_hi = (pgno) >> 16; \
        if (PGNO_TOPWORD) (node)->mn_flags = (pgno) >> PGNO_TOPWORD; } while(0)

        /** Get the size of the data in a leaf node */
#define NODEDSZ(node)    ((node)->mn_lo | ((unsigned)(node)->mn_hi << 16))
        /** Set the size of the data for a leaf node */
#define SETDSZ(node,size)       do { \
        (node)->mn_lo = (size) & 0xffff; (node)->mn_hi = (size) >> 16;} while(0)
        /** The size of a key in a node */
#define NODEKSZ(node)    ((node)->mn_ksize)

        /** Copy a page number from src to dst */
#ifdef MISALIGNED_OK
#define COPY_PGNO(dst,src)      dst = src
#else
#if SIZE_MAX > 4294967295UL
#define COPY_PGNO(dst,src)      do { \
        unsigned short *s, *d;  \
        s = (unsigned short *)&(src);   \
        d = (unsigned short *)&(dst);   \
        *d++ = *s++;    \
        *d++ = *s++;    \
        *d++ = *s++;    \
        *d = *s;        \
} while (0)
#else
#define COPY_PGNO(dst,src)      do { \
        unsigned short *s, *d;  \
        s = (unsigned short *)&(src);   \
        d = (unsigned short *)&(dst);   \
        *d++ = *s++;    \
        *d = *s;        \
} while (0)
#endif
#endif
        /** The address of a key in a LEAF2 page.
         *      LEAF2 pages are used for #MDB_DUPFIXED sorted-duplicate sub-DBs.
         *      There are no node headers, keys are stored contiguously.
         */
#define LEAF2KEY(p, i, ks)      ((char *)(p) + PAGEHDRSZ + ((i)*(ks)))

        /** Set the \b node's key into \b key, if requested. */
#define MDB_GET_KEY(node, key)  { if ((key) != NULL) { \
        (key)->mv_size = NODEKSZ(node); (key)->mv_data = NODEKEY(node); } }

        /** Information about a single database in the environment. */
typedef struct MDB_db {
        uint32_t        md_pad;         /**< also ksize for LEAF2 pages */
        uint16_t        md_flags;       /**< @ref mdb_dbi_open */
        uint16_t        md_depth;       /**< depth of this tree */
        pgno_t          md_branch_pages;        /**< number of internal pages */
        pgno_t          md_leaf_pages;          /**< number of leaf pages */
        pgno_t          md_overflow_pages;      /**< number of overflow pages */
        size_t          md_entries;             /**< number of data items */
        pgno_t          md_root;                /**< the root page of this tree */
} MDB_db;

        /** mdb_dbi_open flags */
#define MDB_VALID       0x8000          /**< DB handle is valid, for me_dbflags */
#define PERSISTENT_FLAGS        (0xffff & ~(MDB_VALID))
#define VALID_FLAGS     (MDB_REVERSEKEY|MDB_DUPSORT|MDB_INTEGERKEY|MDB_DUPFIXED|\
        MDB_INTEGERDUP|MDB_REVERSEDUP|MDB_CREATE)

        /** Handle for the DB used to track free pages. */
#define FREE_DBI        0
        /** Handle for the default DB. */
#define MAIN_DBI        1

        /** Meta page content. */
typedef struct MDB_meta {
                /** Stamp identifying this as an MDB file. It must be set
                 *      to #MDB_MAGIC. */
        uint32_t        mm_magic;
                /** Version number of this lock file. Must be set to #MDB_VERSION. */
        uint32_t        mm_version;
        void            *mm_address;            /**< address for fixed mapping */
        size_t          mm_mapsize;                     /**< size of mmap region */
        MDB_db          mm_dbs[2];                      /**< first is free space, 2nd is main db */
        /** The size of pages used in this DB */
#define mm_psize        mm_dbs[0].md_pad
        /** Any persistent environment flags. @ref mdb_env */
#define mm_flags        mm_dbs[0].md_flags
        pgno_t          mm_last_pg;                     /**< last used page in file */
        txnid_t         mm_txnid;                       /**< txnid that committed this page */
} MDB_meta;

        /** Buffer for a stack-allocated dirty page.
         *      The members define size and alignment, and silence type
         *      aliasing warnings.  They are not used directly; that could
         *      mean incorrectly using several union members in parallel.
         */
typedef union MDB_pagebuf {
        char            mb_raw[MDB_PAGESIZE];
        MDB_page        mb_page;
        struct {
                char            mm_pad[PAGEHDRSZ];
                MDB_meta        mm_meta;
        } mb_metabuf;
} MDB_pagebuf;

        /** Auxiliary DB info.
         *      The information here is mostly static/read-only. There is
         *      only a single copy of this record in the environment.
         */
typedef struct MDB_dbx {
        MDB_val         md_name;                /**< name of the database */
        MDB_cmp_func    *md_cmp;        /**< function for comparing keys */
        MDB_cmp_func    *md_dcmp;       /**< function for comparing data items */
        MDB_rel_func    *md_rel;        /**< user relocate function */
        void            *md_relctx;             /**< user-provided context for md_rel */
} MDB_dbx;

        /** A database transaction.
         *      Every operation requires a transaction handle.
         */
struct MDB_txn {
        MDB_txn         *mt_parent;             /**< parent of a nested txn */
        MDB_txn         *mt_child;              /**< nested txn under this txn */
        pgno_t          mt_next_pgno;   /**< next unallocated page */
        /** The ID of this transaction. IDs are integers incrementing from 1.
         *      Only committed write transactions increment the ID. If a transaction
         *      aborts, the ID may be re-used by the next writer.
         */
        txnid_t         mt_txnid;
        MDB_env         *mt_env;                /**< the DB environment */
        /** The list of pages that became unused during this transaction.
         */
        MDB_IDL         mt_free_pgs;
        /** The list of dirty pages we temporarily wrote to disk
         *      because the dirty list was full.
         */
        MDB_IDL         mt_spill_pgs;
        union {
                MDB_ID2L        dirty_list;     /**< for write txns: modified pages */
                MDB_reader      *reader;        /**< this thread's reader table slot or NULL */
        } mt_u;
        /** Array of records for each DB known in the environment. */
        MDB_dbx         *mt_dbxs;
        /** Array of MDB_db records for each known DB */
        MDB_db          *mt_dbs;
/** @defgroup mt_dbflag Transaction DB Flags
 *      @ingroup internal
 * @{
 */
#define DB_DIRTY        0x01            /**< DB was written in this txn */
#define DB_STALE        0x02            /**< DB record is older than txnID */
#define DB_NEW          0x04            /**< DB handle opened in this txn */
#define DB_VALID        0x08            /**< DB handle is valid, see also #MDB_VALID */
/** @} */
        /** In write txns, array of cursors for each DB */
        MDB_cursor      **mt_cursors;
        /** Array of flags for each DB */
        unsigned char   *mt_dbflags;
        /**     Number of DB records in use. This number only ever increments;
         *      we don't decrement it when individual DB handles are closed.
         */
        MDB_dbi         mt_numdbs;

/** @defgroup mdb_txn   Transaction Flags
 *      @ingroup internal
 *      @{
 */
#define MDB_TXN_RDONLY          0x01            /**< read-only transaction */
#define MDB_TXN_ERROR           0x02            /**< an error has occurred */
#define MDB_TXN_DIRTY           0x04            /**< must write, even if dirty list is empty */
#define MDB_TXN_SPILLS          0x08            /**< txn or a parent has spilled pages */
/** @} */
        unsigned int    mt_flags;               /**< @ref mdb_txn */
        /** dirty_list maxsize - # of allocated pages allowed, including in parent txns */
        unsigned int    mt_dirty_room;
        /** Tracks which of the two meta pages was used at the start
         *      of this transaction.
         */
        unsigned int    mt_toggle;
};

/** Enough space for 2^32 nodes with minimum of 2 keys per node. I.e., plenty.
 * At 4 keys per node, enough for 2^64 nodes, so there's probably no need to
 * raise this on a 64 bit machine.
 */
#define CURSOR_STACK             32

struct MDB_xcursor;

        /** Cursors are used for all DB operations */
struct MDB_cursor {
        /** Next cursor on this DB in this txn */
        MDB_cursor      *mc_next;
        /** Backup of the original cursor if this cursor is a shadow */
        MDB_cursor      *mc_backup;
        /** Context used for databases with #MDB_DUPSORT, otherwise NULL */
        struct MDB_xcursor      *mc_xcursor;
        /** The transaction that owns this cursor */
        MDB_txn         *mc_txn;
        /** The database handle this cursor operates on */
        MDB_dbi         mc_dbi;
        /** The database record for this cursor */
        MDB_db          *mc_db;
        /** The database auxiliary record for this cursor */
        MDB_dbx         *mc_dbx;
        /** The @ref mt_dbflag for this database */
        unsigned char   *mc_dbflag;
        unsigned short  mc_snum;        /**< number of pushed pages */
        unsigned short  mc_top;         /**< index of top page, normally mc_snum-1 */
/** @defgroup mdb_cursor        Cursor Flags
 *      @ingroup internal
 *      Cursor state flags.
 *      @{
 */
#define C_INITIALIZED   0x01    /**< cursor has been initialized and is valid */
#define C_EOF   0x02                    /**< No more data */
#define C_SUB   0x04                    /**< Cursor is a sub-cursor */
#define C_SPLITTING     0x20            /**< Cursor is in page_split */
#define C_UNTRACK       0x40            /**< Un-track cursor when closing */
/** @} */
        unsigned int    mc_flags;       /**< @ref mdb_cursor */
        MDB_page        *mc_pg[CURSOR_STACK];   /**< stack of pushed pages */
        indx_t          mc_ki[CURSOR_STACK];    /**< stack of page indices */
};

        /** Context for sorted-dup records.
         *      We could have gone to a fully recursive design, with arbitrarily
         *      deep nesting of sub-databases. But for now we only handle these
         *      levels - main DB, optional sub-DB, sorted-duplicate DB.
         */
typedef struct MDB_xcursor {
        /** A sub-cursor for traversing the Dup DB */
        MDB_cursor mx_cursor;
        /** The database record for this Dup DB */
        MDB_db  mx_db;
        /**     The auxiliary DB record for this Dup DB */
        MDB_dbx mx_dbx;
        /** The @ref mt_dbflag for this Dup DB */
        unsigned char mx_dbflag;
} MDB_xcursor;

        /** State of FreeDB old pages, stored in the MDB_env */
typedef struct MDB_pgstate {
        pgno_t          *mf_pghead;     /**< Reclaimed freeDB pages, or NULL before use */
        txnid_t         mf_pglast;      /**< ID of last used record, or 0 if !mf_pghead */
} MDB_pgstate;

        /** The database environment. */
struct MDB_env {
        HANDLE          me_fd;          /**< The main data file */
        HANDLE          me_lfd;         /**< The lock file */
        HANDLE          me_mfd;                 /**< just for writing the meta pages */
        /** Failed to update the meta page. Probably an I/O error. */
#define MDB_FATAL_ERROR 0x80000000U
        /** Some fields are initialized. */
#define MDB_ENV_ACTIVE  0x20000000U
        /** me_txkey is set */
#define MDB_ENV_TXKEY   0x10000000U
        uint32_t        me_flags;               /**< @ref mdb_env */
        unsigned int    me_psize;       /**< size of a page, from #GET_PAGESIZE */
        unsigned int    me_maxreaders;  /**< size of the reader table */
        unsigned int    me_numreaders;  /**< max numreaders set by this env */
        MDB_dbi         me_numdbs;              /**< number of DBs opened */
        MDB_dbi         me_maxdbs;              /**< size of the DB table */
        pid_t           me_pid;         /**< process ID of this env */
        char            *me_path;               /**< path to the DB files */
        char            *me_map;                /**< the memory map of the data file */
        MDB_txninfo     *me_txns;               /**< the memory map of the lock file or NULL */
        MDB_meta        *me_metas[2];   /**< pointers to the two meta pages */
        MDB_txn         *me_txn;                /**< current write transaction */
        size_t          me_mapsize;             /**< size of the data memory map */
        off_t           me_size;                /**< current file size */
        pgno_t          me_maxpg;               /**< me_mapsize / me_psize */
        MDB_dbx         *me_dbxs;               /**< array of static DB info */
        uint16_t        *me_dbflags;    /**< array of flags from MDB_db.md_flags */
        pthread_key_t   me_txkey;       /**< thread-key for readers */
        MDB_pgstate     me_pgstate;             /**< state of old pages from freeDB */
#       define          me_pglast       me_pgstate.mf_pglast
#       define          me_pghead       me_pgstate.mf_pghead
        MDB_page        *me_dpages;             /**< list of malloc'd blocks for re-use */
        /** IDL of pages that became unused in a write txn */
        MDB_IDL         me_free_pgs;
        /** ID2L of pages written during a write txn. Length MDB_IDL_UM_SIZE. */
        MDB_ID2L        me_dirty_list;
        /** Max number of freelist items that can fit in a single overflow page */
        int                     me_maxfree_1pg;
        /** Max size of a node on a page */
        unsigned int    me_nodemax;
#ifdef _WIN32
        HANDLE          me_rmutex;              /* Windows mutexes don't reside in shared mem */
        HANDLE          me_wmutex;
#elif defined(MDB_USE_POSIX_SEM)
        sem_t           *me_rmutex;             /* Shared mutexes are not supported */
        sem_t           *me_wmutex;
#endif
};

        /** Nested transaction */
typedef struct MDB_ntxn {
        MDB_txn         mnt_txn;                /* the transaction */
        MDB_pgstate     mnt_pgstate;    /* parent transaction's saved freestate */
} MDB_ntxn;

        /** max number of pages to commit in one writev() call */
#define MDB_COMMIT_PAGES         64
#if defined(IOV_MAX) && IOV_MAX < MDB_COMMIT_PAGES
#undef MDB_COMMIT_PAGES
#define MDB_COMMIT_PAGES        IOV_MAX
#endif

        /* max bytes to write in one call */
#define MAX_WRITE               (0x80000000U >> (sizeof(ssize_t) == 4))

static int  mdb_page_alloc(MDB_cursor *mc, int num, MDB_page **mp);
static int  mdb_page_new(MDB_cursor *mc, uint32_t flags, int num, MDB_page **mp);
static int  mdb_page_touch(MDB_cursor *mc);

static int  mdb_page_get(MDB_txn *txn, pgno_t pgno, MDB_page **mp, int *lvl);
static int  mdb_page_search_root(MDB_cursor *mc,
                            MDB_val *key, int modify);
#define MDB_PS_MODIFY   1
#define MDB_PS_ROOTONLY 2
static int  mdb_page_search(MDB_cursor *mc,
                            MDB_val *key, int flags);
static int      mdb_page_merge(MDB_cursor *csrc, MDB_cursor *cdst);

#define MDB_SPLIT_REPLACE       MDB_APPENDDUP   /**< newkey is not new */
static int      mdb_page_split(MDB_cursor *mc, MDB_val *newkey, MDB_val *newdata,
                                pgno_t newpgno, unsigned int nflags);

static int  mdb_env_read_header(MDB_env *env, MDB_meta *meta);
static int  mdb_env_pick_meta(const MDB_env *env);
static int  mdb_env_write_meta(MDB_txn *txn);
#if !(defined(_WIN32) || defined(MDB_USE_POSIX_SEM)) /* Drop unused excl arg */
# define mdb_env_close0(env, excl) mdb_env_close1(env)
#endif
static void mdb_env_close0(MDB_env *env, int excl);

static MDB_node *mdb_node_search(MDB_cursor *mc, MDB_val *key, int *exactp);
static int  mdb_node_add(MDB_cursor *mc, indx_t indx,
                            MDB_val *key, MDB_val *data, pgno_t pgno, unsigned int flags);
static void mdb_node_del(MDB_page *mp, indx_t indx, int ksize);
static void mdb_node_shrink(MDB_page *mp, indx_t indx);
static int      mdb_node_move(MDB_cursor *csrc, MDB_cursor *cdst);
static int  mdb_node_read(MDB_txn *txn, MDB_node *leaf, MDB_val *data);
static size_t   mdb_leaf_size(MDB_env *env, MDB_val *key, MDB_val *data);
static size_t   mdb_branch_size(MDB_env *env, MDB_val *key);

static int      mdb_rebalance(MDB_cursor *mc);
static int      mdb_update_key(MDB_cursor *mc, MDB_val *key);

static void     mdb_cursor_pop(MDB_cursor *mc);
static int      mdb_cursor_push(MDB_cursor *mc, MDB_page *mp);

static int      mdb_cursor_del0(MDB_cursor *mc, MDB_node *leaf);
static int      mdb_cursor_sibling(MDB_cursor *mc, int move_right);
static int      mdb_cursor_next(MDB_cursor *mc, MDB_val *key, MDB_val *data, MDB_cursor_op op);
static int      mdb_cursor_prev(MDB_cursor *mc, MDB_val *key, MDB_val *data, MDB_cursor_op op);
static int      mdb_cursor_set(MDB_cursor *mc, MDB_val *key, MDB_val *data, MDB_cursor_op op,
                                int *exactp);
static int      mdb_cursor_first(MDB_cursor *mc, MDB_val *key, MDB_val *data);
static int      mdb_cursor_last(MDB_cursor *mc, MDB_val *key, MDB_val *data);

static void     mdb_cursor_init(MDB_cursor *mc, MDB_txn *txn, MDB_dbi dbi, MDB_xcursor *mx);
static void     mdb_xcursor_init0(MDB_cursor *mc);
static void     mdb_xcursor_init1(MDB_cursor *mc, MDB_node *node);

static int      mdb_drop0(MDB_cursor *mc, int subs);
static void mdb_default_cmp(MDB_txn *txn, MDB_dbi dbi);

/** @cond */
static MDB_cmp_func     mdb_cmp_memn, mdb_cmp_memnr, mdb_cmp_int, mdb_cmp_cint, mdb_cmp_long;
/** @endcond */

#ifdef _WIN32
static SECURITY_DESCRIPTOR mdb_null_sd;
static SECURITY_ATTRIBUTES mdb_all_sa;
static int mdb_sec_inited;
#endif

/** Return the library version info. */
char *
mdb_version(int *major, int *minor, int *patch)
{
        if (major) *major = MDB_VERSION_MAJOR;
        if (minor) *minor = MDB_VERSION_MINOR;
        if (patch) *patch = MDB_VERSION_PATCH;
        return MDB_VERSION_STRING;
}

/** Table of descriptions for MDB @ref errors */
static char *const mdb_errstr[] = {
        "MDB_KEYEXIST: Key/data pair already exists",
        "MDB_NOTFOUND: No matching key/data pair found",
        "MDB_PAGE_NOTFOUND: Requested page not found",
        "MDB_CORRUPTED: Located page was wrong type",
        "MDB_PANIC: Update of meta page failed",
        "MDB_VERSION_MISMATCH: Database environment version mismatch",
        "MDB_INVALID: File is not an MDB file",
        "MDB_MAP_FULL: Environment mapsize limit reached",
        "MDB_DBS_FULL: Environment maxdbs limit reached",
        "MDB_READERS_FULL: Environment maxreaders limit reached",
        "MDB_TLS_FULL: Thread-local storage keys full - too many environments open",
        "MDB_TXN_FULL: Transaction has too many dirty pages - transaction too big",
        "MDB_CURSOR_FULL: Internal error - cursor stack limit reached",
        "MDB_PAGE_FULL: Internal error - page has no more space",
        "MDB_MAP_RESIZED: Database contents grew beyond environment mapsize",
        "MDB_INCOMPATIBLE: Database flags changed or would change",
        "MDB_BAD_RSLOT: Invalid reuse of reader locktable slot",
};

char *
mdb_strerror(int err)
{
        int i;
        if (!err)
                return ("Successful return: 0");

        if (err >= MDB_KEYEXIST && err <= MDB_LAST_ERRCODE) {
                i = err - MDB_KEYEXIST;
                return mdb_errstr[i];
        }

        return strerror(err);
}

#if MDB_DEBUG
/** Display a key in hexadecimal and return the address of the result.
 * @param[in] key the key to display
 * @param[in] buf the buffer to write into. Should always be #DKBUF.
 * @return The key in hexadecimal form.
 */
char *
mdb_dkey(MDB_val *key, char *buf)
{
        char *ptr = buf;
        unsigned char *c = key->mv_data;
        unsigned int i;

        if (!key)
                return "";

        if (key->mv_size > MDB_MAXKEYSIZE)
                return "MDB_MAXKEYSIZE";
        /* may want to make this a dynamic check: if the key is mostly
         * printable characters, print it as-is instead of converting to hex.
         */
#if 1
        buf[0] = '\0';
        for (i=0; i<key->mv_size; i++)
                ptr += sprintf(ptr, "%02x", *c++);
#else
        sprintf(buf, "%.*s", key->mv_size, key->mv_data);
#endif
        return buf;
}

/** Display all the keys in the page. */
void
mdb_page_list(MDB_page *mp)
{
        MDB_node *node;
        unsigned int i, nkeys, nsize;
        MDB_val key;
        DKBUF;

        nkeys = NUMKEYS(mp);
        fprintf(stderr, "Page %zu numkeys %d\n", mp->mp_pgno, nkeys);
        for (i=0; i<nkeys; i++) {
                node = NODEPTR(mp, i);
                key.mv_size = node->mn_ksize;
                key.mv_data = node->mn_data;
                nsize = NODESIZE + NODEKSZ(node) + sizeof(indx_t);
                if (IS_BRANCH(mp)) {
                        fprintf(stderr, "key %d: page %zu, %s\n", i, NODEPGNO(node),
                                DKEY(&key));
                } else {
                        if (F_ISSET(node->mn_flags, F_BIGDATA))
                                nsize += sizeof(pgno_t);
                        else
                                nsize += NODEDSZ(node);
                        fprintf(stderr, "key %d: nsize %d, %s\n", i, nsize, DKEY(&key));
                }
        }
}

void
mdb_cursor_chk(MDB_cursor *mc)
{
        unsigned int i;
        MDB_node *node;
        MDB_page *mp;

        if (!mc->mc_snum && !(mc->mc_flags & C_INITIALIZED)) return;
        for (i=0; i<mc->mc_top; i++) {
                mp = mc->mc_pg[i];
                node = NODEPTR(mp, mc->mc_ki[i]);
                if (NODEPGNO(node) != mc->mc_pg[i+1]->mp_pgno)
                        printf("oops!\n");
        }
        if (mc->mc_ki[i] >= NUMKEYS(mc->mc_pg[i]))
                printf("ack!\n");
}
#endif

#if MDB_DEBUG > 2
/** Count all the pages in each DB and in the freelist
 *  and make sure it matches the actual number of pages
 *  being used.
 */
static void mdb_audit(MDB_txn *txn)
{
        MDB_cursor mc;
        MDB_val key, data;
        MDB_ID freecount, count;
        MDB_dbi i;
        int rc;

        freecount = 0;
        mdb_cursor_init(&mc, txn, FREE_DBI, NULL);
        while ((rc = mdb_cursor_get(&mc, &key, &data, MDB_NEXT)) == 0)
                freecount += *(MDB_ID *)data.mv_data;

        count = 0;
        for (i = 0; i<txn->mt_numdbs; i++) {
                MDB_xcursor mx;
                mdb_cursor_init(&mc, txn, i, &mx);
                if (txn->mt_dbs[i].md_root == P_INVALID)
                        continue;
                count += txn->mt_dbs[i].md_branch_pages +
                        txn->mt_dbs[i].md_leaf_pages +
                        txn->mt_dbs[i].md_overflow_pages;
                if (txn->mt_dbs[i].md_flags & MDB_DUPSORT) {
                        mdb_page_search(&mc, NULL, 0);
                        do {
                                unsigned j;
                                MDB_page *mp;
                                mp = mc.mc_pg[mc.mc_top];
                                for (j=0; j<NUMKEYS(mp); j++) {
                                        MDB_node *leaf = NODEPTR(mp, j);
                                        if (leaf->mn_flags & F_SUBDATA) {
                                                MDB_db db;
                                                memcpy(&db, NODEDATA(leaf), sizeof(db));
                                                count += db.md_branch_pages + db.md_leaf_pages +
                                                        db.md_overflow_pages;
                                        }
                                }
                        }
                        while (mdb_cursor_sibling(&mc, 1) == 0);
                }
        }
        if (freecount + count + 2 /* metapages */ != txn->mt_next_pgno) {
                fprintf(stderr, "audit: %lu freecount: %lu count: %lu total: %lu next_pgno: %lu\n",
                        txn->mt_txnid, freecount, count+2, freecount+count+2, txn->mt_next_pgno);
        }
}
#endif

int
mdb_cmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b)
{
        return txn->mt_dbxs[dbi].md_cmp(a, b);
}

int
mdb_dcmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b)
{
        return txn->mt_dbxs[dbi].md_dcmp(a, b);
}

/** Allocate a page.
 * Re-use old malloc'd pages first for singletons, otherwise just malloc.
 */
static MDB_page *
mdb_page_malloc(MDB_txn *txn, unsigned num)
{
        MDB_env *env = txn->mt_env;
        MDB_page *ret = env->me_dpages;
        size_t sz = env->me_psize;
        if (num == 1) {
                if (ret) {
                        VGMEMP_ALLOC(env, ret, sz);
                        VGMEMP_DEFINED(ret, sizeof(ret->mp_next));
                        env->me_dpages = ret->mp_next;
                        return ret;
                }
        } else {
                sz *= num;
        }
        if ((ret = malloc(sz)) != NULL) {
                VGMEMP_ALLOC(env, ret, sz);
        }
        return ret;
}

/** Free a single page.
 * Saves single pages to a list, for future reuse.
 * (This is not used for multi-page overflow pages.)
 */
static void
mdb_page_free(MDB_env *env, MDB_page *mp)
{
        mp->mp_next = env->me_dpages;
        VGMEMP_FREE(env, mp);
        env->me_dpages = mp;
}

/* Free a dirty page */
static void
mdb_dpage_free(MDB_env *env, MDB_page *dp)
{
        if (!IS_OVERFLOW(dp) || dp->mp_pages == 1) {
                mdb_page_free(env, dp);
        } else {
                /* large pages just get freed directly */
                VGMEMP_FREE(env, dp);
                free(dp);
        }
}

/**     Return all dirty pages to dpage list */
static void
mdb_dlist_free(MDB_txn *txn)
{
        MDB_env *env = txn->mt_env;
        MDB_ID2L dl = txn->mt_u.dirty_list;
        unsigned i, n = dl[0].mid;

        for (i = 1; i <= n; i++) {
                mdb_dpage_free(env, dl[i].mptr);
        }
        dl[0].mid = 0;
}

/* Set or clear P_KEEP in non-overflow, non-sub pages in known cursors.
 * When clearing, only consider backup cursors (from parent txns) since
 * other P_KEEP flags have already been cleared.
 * @param[in] mc A cursor handle for the current operation.
 * @param[in] pflags Flags of the pages to update:
 * P_DIRTY to set P_KEEP, P_DIRTY|P_KEEP to clear it.
 */
static void
mdb_cursorpages_mark(MDB_cursor *mc, unsigned pflags)
{
        MDB_txn *txn = mc->mc_txn;
        MDB_cursor *m2, *m3;
        MDB_xcursor *mx;
        unsigned i, j;

        if (mc->mc_flags & C_UNTRACK)
                mc = NULL;                              /* will find mc in mt_cursors */
        for (i = txn->mt_numdbs;; mc = txn->mt_cursors[--i]) {
                for (; mc; mc=mc->mc_next) {
                        m2 = pflags == P_DIRTY ? mc : mc->mc_backup;
                        for (; m2; m2 = m2->mc_backup) {
                                for (m3=m2; m3->mc_flags & C_INITIALIZED; m3=&mx->mx_cursor) {
                                        for (j=0; j<m3->mc_snum; j++)
                                                if ((m3->mc_pg[j]->mp_flags & (P_SUBP|P_DIRTY|P_KEEP))
                                                                == pflags)
                                                        m3->mc_pg[j]->mp_flags ^= P_KEEP;
                                        if (!(m3->mc_db->md_flags & MDB_DUPSORT))
                                                break;
                                        /* Cursor backups have mx malloced at the end of m2 */
                                        mx = (m3 == mc ? m3->mc_xcursor : (MDB_xcursor *)(m3+1));
                                }
                        }
                }
                if (i == 0)
                        break;
        }
}

static int mdb_page_flush(MDB_txn *txn);

/**     Spill pages from the dirty list back to disk.
 * This is intended to prevent running into #MDB_TXN_FULL situations,
 * but note that they may still occur in a few cases:
 *      1) pages in #MDB_DUPSORT sub-DBs are never spilled, so if there
 *       are too many of these dirtied in one txn, the txn may still get
 *       too full.
 *      2) child txns may run out of space if their parents dirtied a
 *       lot of pages and never spilled them. TODO: we probably should do
 *       a preemptive spill during #mdb_txn_begin() of a child txn, if
 *       the parent's dirty_room is below a given threshold.
 *      3) our estimate of the txn size could be too small. At the
 *       moment this seems unlikely.
 *
 * Otherwise, if not using nested txns, it is expected that apps will
 * not run into #MDB_TXN_FULL any more. The pages are flushed to disk
 * the same way as for a txn commit, e.g. their P_DIRTY flag is cleared.
 * If the txn never references them again, they can be left alone.
 * If the txn only reads them, they can be used without any fuss.
 * If the txn writes them again, they can be dirtied immediately without
 * going thru all of the work of #mdb_page_touch(). Such references are
 * handled by #mdb_page_unspill().
 *
 * Also note, we never spill DB root pages, nor pages of active cursors,
 * because we'll need these back again soon anyway. And in nested txns,
 * we can't spill a page in a child txn if it was already spilled in a
 * parent txn. That would alter the parent txns' data even though
 * the child hasn't committed yet, and we'd have no way to undo it if
 * the child aborted.
 *
 * @param[in] m0 cursor A cursor handle identifying the transaction and
 *      database for which we are checking space.
 * @param[in] key For a put operation, the key being stored.
 * @param[in] data For a put operation, the data being stored.
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_page_spill(MDB_cursor *m0, MDB_val *key, MDB_val *data)
{
        MDB_txn *txn = m0->mc_txn;
        MDB_page *dp;
        MDB_ID2L dl = txn->mt_u.dirty_list;
        unsigned int i, j;
        int rc;

        if (m0->mc_flags & C_SUB)
                return MDB_SUCCESS;

        /* Estimate how much space this op will take */
        i = m0->mc_db->md_depth;
        /* Named DBs also dirty the main DB */
        if (m0->mc_dbi > MAIN_DBI)
                i += txn->mt_dbs[MAIN_DBI].md_depth;
        /* For puts, roughly factor in the key+data size */
        if (key)
                i += (LEAFSIZE(key, data) + txn->mt_env->me_psize) / txn->mt_env->me_psize;
        i += i; /* double it for good measure */

        if (txn->mt_dirty_room > i)
                return MDB_SUCCESS;

        if (!txn->mt_spill_pgs) {
                txn->mt_spill_pgs = mdb_midl_alloc(MDB_IDL_UM_MAX);
                if (!txn->mt_spill_pgs)
                        return ENOMEM;
        }

        /* Mark all the dirty root pages we want to preserve */
        for (i=0; i<txn->mt_numdbs; i++) {
                if (txn->mt_dbflags[i] & DB_DIRTY) {
                        j = mdb_mid2l_search(dl, txn->mt_dbs[i].md_root);
                        if (j <= dl[0].mid) {
                                dp = dl[j].mptr;
                                dp->mp_flags |= P_KEEP;
                        }
                }
        }

        /* Preserve pages used by cursors */
        mdb_cursorpages_mark(m0, P_DIRTY);

        /* Save the page IDs of all the pages we're flushing */
        for (i=1; i<=dl[0].mid; i++) {
                dp = dl[i].mptr;
                if (dp->mp_flags & P_KEEP)
                        continue;
                /* Can't spill twice, make sure it's not already in a parent's
                 * spill list.
                 */
                if (txn->mt_parent) {
                        MDB_txn *tx2;
                        for (tx2 = txn->mt_parent; tx2; tx2 = tx2->mt_parent) {
                                if (tx2->mt_spill_pgs) {
                                        j = mdb_midl_search(tx2->mt_spill_pgs, dl[i].mid);
                                        if (j <= tx2->mt_spill_pgs[0] && tx2->mt_spill_pgs[j] == dl[i].mid) {
                                                dp->mp_flags |= P_KEEP;
                                                break;
                                        }
                                }
                        }
                        if (tx2)
                                continue;
                }
                if ((rc = mdb_midl_append(&txn->mt_spill_pgs, dl[i].mid)))
                        return rc;
        }
        mdb_midl_sort(txn->mt_spill_pgs);

        rc = mdb_page_flush(txn);

        mdb_cursorpages_mark(m0, P_DIRTY|P_KEEP);

        if (rc == 0) {
                txn->mt_dirty_room = MDB_IDL_UM_MAX - dl[0].mid;
                txn->mt_flags |= MDB_TXN_SPILLS;
        }
        return rc;
}

/** Find oldest txnid still referenced. Expects txn->mt_txnid > 0. */
static txnid_t
mdb_find_oldest(MDB_txn *txn)
{
        int i;
        txnid_t mr, oldest = txn->mt_txnid - 1;
        MDB_reader *r = txn->mt_env->me_txns->mti_readers;
        for (i = txn->mt_env->me_txns->mti_numreaders; --i >= 0; ) {
                if (r[i].mr_pid) {
                        mr = r[i].mr_txnid;
                        if (oldest > mr)
                                oldest = mr;
                }
        }
        return oldest;
}

/** Add a page to the txn's dirty list */
static void
mdb_page_dirty(MDB_txn *txn, MDB_page *mp)
{
        MDB_ID2 mid;
        int (*insert)(MDB_ID2L, MDB_ID2 *);

        if (txn->mt_env->me_flags & MDB_WRITEMAP) {
                insert = mdb_mid2l_append;
        } else {
                insert = mdb_mid2l_insert;
        }
        mid.mid = mp->mp_pgno;
        mid.mptr = mp;
        insert(txn->mt_u.dirty_list, &mid);
        txn->mt_dirty_room--;
}

/** Allocate pages for writing.
 * If there are free pages available from older transactions, they
 * will be re-used first. Otherwise a new page will be allocated.
 * @param[in] mc cursor A cursor handle identifying the transaction and
 *      database for which we are allocating.
 * @param[in] num the number of pages to allocate.
 * @param[out] mp Address of the allocated page(s). Requests for multiple pages
 *  will always be satisfied by a single contiguous chunk of memory.
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_page_alloc(MDB_cursor *mc, int num, MDB_page **mp)
{
#ifdef MDB_PARANOID     /* Seems like we can ignore this now */
        /* Get at most <Max_retries> more freeDB records once me_pghead
         * has enough pages.  If not enough, use new pages from the map.
         * If <Paranoid> and mc is updating the freeDB, only get new
         * records if me_pghead is empty. Then the freelist cannot play
         * catch-up with itself by growing while trying to save it.
         */
        enum { Paranoid = 1, Max_retries = 500 };
#else
        enum { Paranoid = 0, Max_retries = INT_MAX /*infinite*/ };
#endif
        int rc, n2 = num-1, retry = Max_retries;
        MDB_txn *txn = mc->mc_txn;
        MDB_env *env = txn->mt_env;
        pgno_t pgno, *mop = env->me_pghead;
        unsigned i, j, k, mop_len = mop ? mop[0] : 0;
        MDB_page *np;
        txnid_t oldest = 0, last;
        MDB_cursor_op op;
        MDB_cursor m2;

        *mp = NULL;

        /* If our dirty list is already full, we can't do anything */
        if (txn->mt_dirty_room == 0)
                return MDB_TXN_FULL;

        for (op = MDB_FIRST;; op = MDB_NEXT) {
                MDB_val key, data;
                MDB_node *leaf;
                pgno_t *idl, old_id, new_id;

                /* Seek a big enough contiguous page range. Prefer
                 * pages at the tail, just truncating the list.
                 */
                if (mop_len >= (unsigned)num) {
                        i = mop_len;
                        do {
                                pgno = mop[i];
                                if (mop[i-n2] == pgno+n2)
                                        goto search_done;
                        } while (--i >= (unsigned)num);
                        if (Max_retries < INT_MAX && --retry < 0)
                                break;
                }

                if (op == MDB_FIRST) {  /* 1st iteration */
                        /* Prepare to fetch more and coalesce */
                        oldest = mdb_find_oldest(txn);
                        last = env->me_pglast;
                        mdb_cursor_init(&m2, txn, FREE_DBI, NULL);
                        if (last) {
                                op = MDB_SET_RANGE;
                                key.mv_data = &last; /* will loop up last+1 */
                                key.mv_size = sizeof(last);
                        }
                        if (Paranoid && mc->mc_dbi == FREE_DBI)
                                retry = -1;
                }
                if (Paranoid && retry < 0 && mop_len)
                        break;

                last++;
                /* Do not fetch more if the record will be too recent */
                if (oldest <= last)
                        break;
                rc = mdb_cursor_get(&m2, &key, NULL, op);
                if (rc) {
                        if (rc == MDB_NOTFOUND)
                                break;
                        return rc;
                }
                last = *(txnid_t*)key.mv_data;
                if (oldest <= last)
                        break;
                np = m2.mc_pg[m2.mc_top];
                leaf = NODEPTR(np, m2.mc_ki[m2.mc_top]);
                if ((rc = mdb_node_read(txn, leaf, &data)) != MDB_SUCCESS)
                        return rc;

                idl = (MDB_ID *) data.mv_data;
                i = idl[0];
                if (!mop) {
                        if (!(env->me_pghead = mop = mdb_midl_alloc(i)))
                                return ENOMEM;
                } else {
                        if ((rc = mdb_midl_need(&env->me_pghead, i)) != 0)
                                return rc;
                        mop = env->me_pghead;
                }
                env->me_pglast = last;
#if MDB_DEBUG > 1
                DPRINTF("IDL read txn %zu root %zu num %u",
                                last, txn->mt_dbs[FREE_DBI].md_root, i);
                for (k = i; k; k--)
                        DPRINTF("IDL %zu", idl[k]);
#endif
                /* Merge in descending sorted order */
                j = mop_len;
                k = mop_len += i;
                mop[0] = (pgno_t)-1;
                old_id = mop[j];
                while (i) {
                        new_id = idl[i--];
                        for (; old_id < new_id; old_id = mop[--j])
                                mop[k--] = old_id;
                        mop[k--] = new_id;
                }
                mop[0] = mop_len;
        }

        /* Use new pages from the map when nothing suitable in the freeDB */
        i = 0;
        pgno = txn->mt_next_pgno;
        if (pgno + num >= env->me_maxpg) {
                        DPUTS("DB size maxed out");
                        return MDB_MAP_FULL;
        }

search_done:
        if (env->me_flags & MDB_WRITEMAP) {
                np = (MDB_page *)(env->me_map + env->me_psize * pgno);
        } else {
                if (!(np = mdb_page_malloc(txn, num)))
                        return ENOMEM;
        }
        if (i) {
                mop[0] = mop_len -= num;
                /* Move any stragglers down */
                for (j = i-num; j < mop_len; )
                        mop[++j] = mop[++i];
        } else {
                txn->mt_next_pgno = pgno + num;
        }
        np->mp_pgno = pgno;
        mdb_page_dirty(txn, np);
        *mp = np;

        return MDB_SUCCESS;
}

/** Copy the used portions of a non-overflow page.
 * @param[in] dst page to copy into
 * @param[in] src page to copy from
 * @param[in] psize size of a page
 */
static void
mdb_page_copy(MDB_page *dst, MDB_page *src, unsigned int psize)
{
        enum { Align = sizeof(pgno_t) };
        indx_t upper = src->mp_upper, lower = src->mp_lower, unused = upper-lower;

        /* If page isn't full, just copy the used portion. Adjust
         * alignment so memcpy may copy words instead of bytes.
         */
        if ((unused &= -Align) && !IS_LEAF2(src)) {
                upper &= -Align;
                memcpy(dst, src, (lower + (Align-1)) & -Align);
                memcpy((pgno_t *)((char *)dst+upper), (pgno_t *)((char *)src+upper),
                        psize - upper);
        } else {
                memcpy(dst, src, psize - unused);
        }
}

/** Pull a page off the txn's spill list, if present.
 * If a page being referenced was spilled to disk in this txn, bring
 * it back and make it dirty/writable again.
 * @param[in] tx0 the transaction handle.
 * @param[in] mp the page being referenced.
 * @param[out] ret the writable page, if any. ret is unchanged if
 * mp wasn't spilled.
 */
static int
mdb_page_unspill(MDB_txn *tx0, MDB_page *mp, MDB_page **ret)
{
        MDB_env *env = tx0->mt_env;
        MDB_txn *txn;
        unsigned x;
        pgno_t pgno = mp->mp_pgno;

        for (txn = tx0; txn; txn=txn->mt_parent) {
                if (!txn->mt_spill_pgs)
                        continue;
                x = mdb_midl_search(txn->mt_spill_pgs, pgno);
                if (x <= txn->mt_spill_pgs[0] && txn->mt_spill_pgs[x] == pgno) {
                        MDB_page *np;
                        int num;
                        if (IS_OVERFLOW(mp))
                                num = mp->mp_pages;
                        else
                                num = 1;
                        if (env->me_flags & MDB_WRITEMAP) {
                                np = mp;
                        } else {
                                np = mdb_page_malloc(txn, num);
                                if (!np)
                                        return ENOMEM;
                                if (num > 1)
                                        memcpy(np, mp, num * env->me_psize);
                                else
                                        mdb_page_copy(np, mp, env->me_psize);
                        }
                        if (txn == tx0) {
                                /* If in current txn, this page is no longer spilled */
                                for (; x < txn->mt_spill_pgs[0]; x++)
                                        txn->mt_spill_pgs[x] = txn->mt_spill_pgs[x+1];
                                txn->mt_spill_pgs[0]--;
                        }       /* otherwise, if belonging to a parent txn, the
                                 * page remains spilled until child commits
                                 */
                        mdb_page_dirty(tx0, np);
                        np->mp_flags |= P_DIRTY;
                        *ret = np;
                        break;
                }
        }
        return MDB_SUCCESS;
}

/** Touch a page: make it dirty and re-insert into tree with updated pgno.
 * @param[in] mc cursor pointing to the page to be touched
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_page_touch(MDB_cursor *mc)
{
        MDB_page *mp = mc->mc_pg[mc->mc_top], *np;
        MDB_txn *txn = mc->mc_txn;
        MDB_cursor *m2, *m3;
        MDB_dbi dbi;
        pgno_t  pgno;
        int rc;

        if (!F_ISSET(mp->mp_flags, P_DIRTY)) {
                if (txn->mt_flags & MDB_TXN_SPILLS) {
                        np = NULL;
                        rc = mdb_page_unspill(txn, mp, &np);
                        if (rc)
                                return rc;
                        if (np)
                                goto done;
                }
                if ((rc = mdb_midl_need(&txn->mt_free_pgs, 1)) ||
                        (rc = mdb_page_alloc(mc, 1, &np)))
                        return rc;
                pgno = np->mp_pgno;
                DPRINTF("touched db %u page %zu -> %zu", mc->mc_dbi,mp->mp_pgno,pgno);
                assert(mp->mp_pgno != pgno);
                mdb_midl_xappend(txn->mt_free_pgs, mp->mp_pgno);
                /* Update the parent page, if any, to point to the new page */
                if (mc->mc_top) {
                        MDB_page *parent = mc->mc_pg[mc->mc_top-1];
                        MDB_node *node = NODEPTR(parent, mc->mc_ki[mc->mc_top-1]);
                        SETPGNO(node, pgno);
                } else {
                        mc->mc_db->md_root = pgno;
                }
        } else if (txn->mt_parent && !IS_SUBP(mp)) {
                MDB_ID2 mid, *dl = txn->mt_u.dirty_list;
                pgno = mp->mp_pgno;
                /* If txn has a parent, make sure the page is in our
                 * dirty list.
                 */
                if (dl[0].mid) {
                        unsigned x = mdb_mid2l_search(dl, pgno);
                        if (x <= dl[0].mid && dl[x].mid == pgno) {
                                if (mp != dl[x].mptr) { /* bad cursor? */
                                        mc->mc_flags &= ~(C_INITIALIZED|C_EOF);
                                        return MDB_CORRUPTED;
                                }
                                return 0;
                        }
                }
                assert(dl[0].mid < MDB_IDL_UM_MAX);
                /* No - copy it */
                np = mdb_page_malloc(txn, 1);
                if (!np)
                        return ENOMEM;
                mid.mid = pgno;
                mid.mptr = np;
                mdb_mid2l_insert(dl, &mid);
        } else {
                return 0;
        }

        mdb_page_copy(np, mp, txn->mt_env->me_psize);
        np->mp_pgno = pgno;
        np->mp_flags |= P_DIRTY;

done:
        /* Adjust cursors pointing to mp */
        mc->mc_pg[mc->mc_top] = np;
        dbi = mc->mc_dbi;
        if (mc->mc_flags & C_SUB) {
                dbi--;
                for (m2 = txn->mt_cursors[dbi]; m2; m2=m2->mc_next) {
                        m3 = &m2->mc_xcursor->mx_cursor;
                        if (m3->mc_snum < mc->mc_snum) continue;
                        if (m3->mc_pg[mc->mc_top] == mp)
                                m3->mc_pg[mc->mc_top] = np;
                }
        } else {
                for (m2 = txn->mt_cursors[dbi]; m2; m2=m2->mc_next) {
                        if (m2->mc_snum < mc->mc_snum) continue;
                        if (m2->mc_pg[mc->mc_top] == mp) {
                                m2->mc_pg[mc->mc_top] = np;
                                if ((mc->mc_db->md_flags & MDB_DUPSORT) &&
                                        m2->mc_ki[mc->mc_top] == mc->mc_ki[mc->mc_top])
                                {
                                        MDB_node *leaf = NODEPTR(np, mc->mc_ki[mc->mc_top]);
                                        if (!(leaf->mn_flags & F_SUBDATA))
                                                m2->mc_xcursor->mx_cursor.mc_pg[0] = NODEDATA(leaf);
                                }
                        }
                }
        }
        return 0;
}

int
mdb_env_sync(MDB_env *env, int force)
{
        int rc = 0;
        if (force || !F_ISSET(env->me_flags, MDB_NOSYNC)) {
                if (env->me_flags & MDB_WRITEMAP) {
                        int flags = ((env->me_flags & MDB_MAPASYNC) && !force)
                                ? MS_ASYNC : MS_SYNC;
                        if (MDB_MSYNC(env->me_map, env->me_mapsize, flags))
                                rc = ErrCode();
#ifdef _WIN32
                        else if (flags == MS_SYNC && MDB_FDATASYNC(env->me_fd))
                                rc = ErrCode();
#endif
                } else {
                        if (MDB_FDATASYNC(env->me_fd))
                                rc = ErrCode();
                }
        }
        return rc;
}

/** Back up parent txn's cursors, then grab the originals for tracking */
static int
mdb_cursor_shadow(MDB_txn *src, MDB_txn *dst)
{
        MDB_cursor *mc, *bk;
        MDB_xcursor *mx;
        size_t size;
        int i;

        for (i = src->mt_numdbs; --i >= 0; ) {
                if ((mc = src->mt_cursors[i]) != NULL) {
                        size = sizeof(MDB_cursor);
                        if (mc->mc_xcursor)
                                size += sizeof(MDB_xcursor);
                        for (; mc; mc = bk->mc_next) {
                                bk = malloc(size);
                                if (!bk)
                                        return ENOMEM;
                                *bk = *mc;
                                mc->mc_backup = bk;
                                mc->mc_db = &dst->mt_dbs[i];
                                /* Kill pointers into src - and dst to reduce abuse: The
                                 * user may not use mc until dst ends. Otherwise we'd...
                                 */
                                mc->mc_txn    = NULL;   /* ...set this to dst */
                                mc->mc_dbflag = NULL;   /* ...and &dst->mt_dbflags[i] */
                                if ((mx = mc->mc_xcursor) != NULL) {
                                        *(MDB_xcursor *)(bk+1) = *mx;
                                        mx->mx_cursor.mc_txn = NULL; /* ...and dst. */
                                }
                                mc->mc_next = dst->mt_cursors[i];
                                dst->mt_cursors[i] = mc;
                        }
                }
        }
        return MDB_SUCCESS;
}

/** Close this write txn's cursors, give parent txn's cursors back to parent.
 * @param[in] txn the transaction handle.
 * @param[in] merge true to keep changes to parent cursors, false to revert.
 * @return 0 on success, non-zero on failure.
 */
static void
mdb_cursors_close(MDB_txn *txn, unsigned merge)
{
        MDB_cursor **cursors = txn->mt_cursors, *mc, *next, *bk;
        MDB_xcursor *mx;
        int i;

        for (i = txn->mt_numdbs; --i >= 0; ) {
                for (mc = cursors[i]; mc; mc = next) {
                        next = mc->mc_next;
                        if ((bk = mc->mc_backup) != NULL) {
                                if (merge) {
                                        /* Commit changes to parent txn */
                                        mc->mc_next = bk->mc_next;
                                        mc->mc_backup = bk->mc_backup;
                                        mc->mc_txn = bk->mc_txn;
                                        mc->mc_db = bk->mc_db;
                                        mc->mc_dbflag = bk->mc_dbflag;
                                        if ((mx = mc->mc_xcursor) != NULL)
                                                mx->mx_cursor.mc_txn = bk->mc_txn;
                                } else {
                                        /* Abort nested txn */
                                        *mc = *bk;
                                        if ((mx = mc->mc_xcursor) != NULL)
                                                *mx = *(MDB_xcursor *)(bk+1);
                                }
                                mc = bk;
                        }
                        free(mc);
                }
                cursors[i] = NULL;
        }
}

#ifdef MDB_DEBUG_SKIP
#define mdb_txn_reset0(txn, act) mdb_txn_reset0(txn)
#endif
static void
mdb_txn_reset0(MDB_txn *txn, const char *act);

/** Common code for #mdb_txn_begin() and #mdb_txn_renew().
 * @param[in] txn the transaction handle to initialize
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_txn_renew0(MDB_txn *txn)
{
        MDB_env *env = txn->mt_env;
        unsigned int i;
        uint16_t x;
        int rc, new_notls = 0;

        /* Setup db info */
        txn->mt_numdbs = env->me_numdbs;
        txn->mt_dbxs = env->me_dbxs;    /* mostly static anyway */

        if (txn->mt_flags & MDB_TXN_RDONLY) {
                if (!env->me_txns) {
                        i = mdb_env_pick_meta(env);
                        txn->mt_txnid = env->me_metas[i]->mm_txnid;
                        txn->mt_u.reader = NULL;
                } else {
                        MDB_reader *r = (env->me_flags & MDB_NOTLS) ? txn->mt_u.reader :
                                pthread_getspecific(env->me_txkey);
                        if (r) {
                                if (r->mr_pid != env->me_pid || r->mr_txnid != (txnid_t)-1)
                                        return MDB_BAD_RSLOT;
                        } else {
                                pid_t pid = env->me_pid;
                                pthread_t tid = pthread_self();

                                LOCK_MUTEX_R(env);
                                for (i=0; i<env->me_txns->mti_numreaders; i++)
                                        if (env->me_txns->mti_readers[i].mr_pid == 0)
                                                break;
                                if (i == env->me_maxreaders) {
                                        UNLOCK_MUTEX_R(env);
                                        return MDB_READERS_FULL;
                                }
                                env->me_txns->mti_readers[i].mr_pid = pid;
                                env->me_txns->mti_readers[i].mr_tid = tid;
                                if (i >= env->me_txns->mti_numreaders)
                                        env->me_txns->mti_numreaders = i+1;
                                /* Save numreaders for un-mutexed mdb_env_close() */
                                env->me_numreaders = env->me_txns->mti_numreaders;
                                UNLOCK_MUTEX_R(env);
                                r = &env->me_txns->mti_readers[i];
                                new_notls = (env->me_flags & MDB_NOTLS);
                                if (!new_notls && (rc=pthread_setspecific(env->me_txkey, r))) {
                                        r->mr_pid = 0;
                                        return rc;
                                }
                        }
                        txn->mt_txnid = r->mr_txnid = env->me_txns->mti_txnid;
                        txn->mt_u.reader = r;
                }
                txn->mt_toggle = txn->mt_txnid & 1;
        } else {
                LOCK_MUTEX_W(env);

                txn->mt_txnid = env->me_txns->mti_txnid;
                txn->mt_toggle = txn->mt_txnid & 1;
                txn->mt_txnid++;
#if MDB_DEBUG
                if (txn->mt_txnid == mdb_debug_start)
                        mdb_debug = 1;
#endif
                txn->mt_dirty_room = MDB_IDL_UM_MAX;
                txn->mt_u.dirty_list = env->me_dirty_list;
                txn->mt_u.dirty_list[0].mid = 0;
                txn->mt_free_pgs = env->me_free_pgs;
                txn->mt_free_pgs[0] = 0;
                txn->mt_spill_pgs = NULL;
                env->me_txn = txn;
        }

        /* Copy the DB info and flags */
        memcpy(txn->mt_dbs, env->me_metas[txn->mt_toggle]->mm_dbs, 2 * sizeof(MDB_db));

        /* Moved to here to avoid a data race in read TXNs */
        txn->mt_next_pgno = env->me_metas[txn->mt_toggle]->mm_last_pg+1;

        for (i=2; i<txn->mt_numdbs; i++) {
                x = env->me_dbflags[i];
                txn->mt_dbs[i].md_flags = x & PERSISTENT_FLAGS;
                txn->mt_dbflags[i] = (x & MDB_VALID) ? DB_VALID|DB_STALE : 0;
        }
        txn->mt_dbflags[0] = txn->mt_dbflags[1] = DB_VALID;

        if (env->me_maxpg < txn->mt_next_pgno) {
                mdb_txn_reset0(txn, "renew0-mapfail");
                if (new_notls) {
                        txn->mt_u.reader->mr_pid = 0;
                        txn->mt_u.reader = NULL;
                }
                return MDB_MAP_RESIZED;
        }

        return MDB_SUCCESS;
}

int
mdb_txn_renew(MDB_txn *txn)
{
        int rc;

        if (!txn || txn->mt_dbxs)       /* A reset txn has mt_dbxs==NULL */
                return EINVAL;

        if (txn->mt_env->me_flags & MDB_FATAL_ERROR) {
                DPUTS("environment had fatal error, must shutdown!");
                return MDB_PANIC;
        }

        rc = mdb_txn_renew0(txn);
        if (rc == MDB_SUCCESS) {
                DPRINTF("renew txn %zu%c %p on mdbenv %p, root page %zu",
                        txn->mt_txnid, (txn->mt_flags & MDB_TXN_RDONLY) ? 'r' : 'w',
                        (void *)txn, (void *)txn->mt_env, txn->mt_dbs[MAIN_DBI].md_root);
        }
        return rc;
}

int
mdb_txn_begin(MDB_env *env, MDB_txn *parent, unsigned int flags, MDB_txn **ret)
{
        MDB_txn *txn;
        MDB_ntxn *ntxn;
        int rc, size, tsize = sizeof(MDB_txn);

        if (env->me_flags & MDB_FATAL_ERROR) {
                DPUTS("environment had fatal error, must shutdown!");
                return MDB_PANIC;
        }
        if ((env->me_flags & MDB_RDONLY) && !(flags & MDB_RDONLY))
                return EACCES;
        if (parent) {
                /* Nested transactions: Max 1 child, write txns only, no writemap */
                if (parent->mt_child ||
                        (flags & MDB_RDONLY) || (parent->mt_flags & MDB_TXN_RDONLY) ||
                        (env->me_flags & MDB_WRITEMAP))
                {
                        return EINVAL;
                }
                tsize = sizeof(MDB_ntxn);
        }
        size = tsize + env->me_maxdbs * (sizeof(MDB_db)+1);
        if (!(flags & MDB_RDONLY))
                size += env->me_maxdbs * sizeof(MDB_cursor *);

        if ((txn = calloc(1, size)) == NULL) {
                DPRINTF("calloc: %s", strerror(ErrCode()));
                return ENOMEM;
        }
        txn->mt_dbs = (MDB_db *) ((char *)txn + tsize);
        if (flags & MDB_RDONLY) {
                txn->mt_flags |= MDB_TXN_RDONLY;
                txn->mt_dbflags = (unsigned char *)(txn->mt_dbs + env->me_maxdbs);
        } else {
                txn->mt_cursors = (MDB_cursor **)(txn->mt_dbs + env->me_maxdbs);
                txn->mt_dbflags = (unsigned char *)(txn->mt_cursors + env->me_maxdbs);
        }
        txn->mt_env = env;

        if (parent) {
                unsigned int i;
                txn->mt_u.dirty_list = malloc(sizeof(MDB_ID2)*MDB_IDL_UM_SIZE);
                if (!txn->mt_u.dirty_list ||
                        !(txn->mt_free_pgs = mdb_midl_alloc(MDB_IDL_UM_MAX)))
                {
                        free(txn->mt_u.dirty_list);
                        free(txn);
                        return ENOMEM;
                }
                txn->mt_txnid = parent->mt_txnid;
                txn->mt_toggle = parent->mt_toggle;
                txn->mt_dirty_room = parent->mt_dirty_room;
                txn->mt_u.dirty_list[0].mid = 0;
                txn->mt_spill_pgs = NULL;
                txn->mt_next_pgno = parent->mt_next_pgno;
                parent->mt_child = txn;
                txn->mt_parent = parent;
                txn->mt_numdbs = parent->mt_numdbs;
                txn->mt_flags = parent->mt_flags;
                txn->mt_dbxs = parent->mt_dbxs;
                memcpy(txn->mt_dbs, parent->mt_dbs, txn->mt_numdbs * sizeof(MDB_db));
                /* Copy parent's mt_dbflags, but clear DB_NEW */
                for (i=0; i<txn->mt_numdbs; i++)
                        txn->mt_dbflags[i] = parent->mt_dbflags[i] & ~DB_NEW;
                rc = 0;
                ntxn = (MDB_ntxn *)txn;
                ntxn->mnt_pgstate = env->me_pgstate; /* save parent me_pghead & co */
                if (env->me_pghead) {
                        size = MDB_IDL_SIZEOF(env->me_pghead);
                        env->me_pghead = mdb_midl_alloc(env->me_pghead[0]);
                        if (env->me_pghead)
                                memcpy(env->me_pghead, ntxn->mnt_pgstate.mf_pghead, size);
                        else
                                rc = ENOMEM;
                }
                if (!rc)
                        rc = mdb_cursor_shadow(parent, txn);
                if (rc)
                        mdb_txn_reset0(txn, "beginchild-fail");
        } else {
                rc = mdb_txn_renew0(txn);
        }
        if (rc)
                free(txn);
        else {
                *ret = txn;
                DPRINTF("begin txn %zu%c %p on mdbenv %p, root page %zu",
                        txn->mt_txnid, (txn->mt_flags & MDB_TXN_RDONLY) ? 'r' : 'w',
                        (void *) txn, (void *) env, txn->mt_dbs[MAIN_DBI].md_root);
        }

        return rc;
}

/** Export or close DBI handles opened in this txn. */
static void
mdb_dbis_update(MDB_txn *txn, int keep)
{
        int i;
        MDB_dbi n = txn->mt_numdbs;
        MDB_env *env = txn->mt_env;
        unsigned char *tdbflags = txn->mt_dbflags;

        for (i = n; --i >= 2;) {
                if (tdbflags[i] & DB_NEW) {
                        if (keep) {
                                env->me_dbflags[i] = txn->mt_dbs[i].md_flags | MDB_VALID;
                        } else {
                                char *ptr = env->me_dbxs[i].md_name.mv_data;
                                env->me_dbxs[i].md_name.mv_data = NULL;
                                env->me_dbxs[i].md_name.mv_size = 0;
                                env->me_dbflags[i] = 0;
                                free(ptr);
                        }
                }
        }
        if (keep && env->me_numdbs < n)
                env->me_numdbs = n;
}

/** Common code for #mdb_txn_reset() and #mdb_txn_abort().
 * May be called twice for readonly txns: First reset it, then abort.
 * @param[in] txn the transaction handle to reset
 */
static void
mdb_txn_reset0(MDB_txn *txn, const char *act)
{
        MDB_env *env = txn->mt_env;

        /* Close any DBI handles opened in this txn */
        mdb_dbis_update(txn, 0);

        DPRINTF("%s txn %zu%c %p on mdbenv %p, root page %zu",
                act, txn->mt_txnid, (txn->mt_flags & MDB_TXN_RDONLY) ? 'r' : 'w',
                (void *) txn, (void *)env, txn->mt_dbs[MAIN_DBI].md_root);

        if (F_ISSET(txn->mt_flags, MDB_TXN_RDONLY)) {
                if (txn->mt_u.reader) {
                        txn->mt_u.reader->mr_txnid = (txnid_t)-1;
                        if (!(env->me_flags & MDB_NOTLS))
                                txn->mt_u.reader = NULL; /* txn does not own reader */
                }
                txn->mt_numdbs = 0;             /* close nothing if called again */
                txn->mt_dbxs = NULL;    /* mark txn as reset */
        } else {
                mdb_cursors_close(txn, 0);

                if (!(env->me_flags & MDB_WRITEMAP)) {
                        mdb_dlist_free(txn);
                }
                mdb_midl_free(env->me_pghead);

                if (txn->mt_parent) {
                        txn->mt_parent->mt_child = NULL;
                        env->me_pgstate = ((MDB_ntxn *)txn)->mnt_pgstate;
                        mdb_midl_free(txn->mt_free_pgs);
                        mdb_midl_free(txn->mt_spill_pgs);
                        free(txn->mt_u.dirty_list);
                        return;
                }

                if (mdb_midl_shrink(&txn->mt_free_pgs))
                        env->me_free_pgs = txn->mt_free_pgs;
                env->me_pghead = NULL;
                env->me_pglast = 0;

                env->me_txn = NULL;
                /* The writer mutex was locked in mdb_txn_begin. */
                UNLOCK_MUTEX_W(env);
        }
}

void
mdb_txn_reset(MDB_txn *txn)
{
        if (txn == NULL)
                return;

        /* This call is only valid for read-only txns */
        if (!(txn->mt_flags & MDB_TXN_RDONLY))
                return;

        mdb_txn_reset0(txn, "reset");
}

void
mdb_txn_abort(MDB_txn *txn)
{
        if (txn == NULL)
                return;

        if (txn->mt_child)
                mdb_txn_abort(txn->mt_child);

        mdb_txn_reset0(txn, "abort");
        /* Free reader slot tied to this txn (if MDB_NOTLS && writable FS) */
        if ((txn->mt_flags & MDB_TXN_RDONLY) && txn->mt_u.reader)
                txn->mt_u.reader->mr_pid = 0;

        free(txn);
}

/** Save the freelist as of this transaction to the freeDB.
 * This changes the freelist. Keep trying until it stabilizes.
 */
static int
mdb_freelist_save(MDB_txn *txn)
{
        /* env->me_pghead[] can grow and shrink during this call.
         * env->me_pglast and txn->mt_free_pgs[] can only grow.
         * Page numbers cannot disappear from txn->mt_free_pgs[].
         */
        MDB_cursor mc;
        MDB_env *env = txn->mt_env;
        int rc, maxfree_1pg = env->me_maxfree_1pg, more = 1;
        txnid_t pglast = 0, head_id = 0;
        pgno_t  freecnt = 0, *free_pgs, *mop;
        ssize_t head_room = 0, total_room = 0, mop_len;

        mdb_cursor_init(&mc, txn, FREE_DBI, NULL);

        if (env->me_pghead) {
                /* Make sure first page of freeDB is touched and on freelist */
                rc = mdb_page_search(&mc, NULL, MDB_PS_MODIFY);
                if (rc && rc != MDB_NOTFOUND)
                        return rc;
        }

        for (;;) {
                /* Come back here after each Put() in case freelist changed */
                MDB_val key, data;

                /* If using records from freeDB which we have not yet
                 * deleted, delete them and any we reserved for me_pghead.
                 */
                while (pglast < env->me_pglast) {
                        rc = mdb_cursor_first(&mc, &key, NULL);
                        if (rc)
                                return rc;
                        pglast = head_id = *(txnid_t *)key.mv_data;
                        total_room = head_room = 0;
                        assert(pglast <= env->me_pglast);
                        rc = mdb_cursor_del(&mc, 0);
                        if (rc)
                                return rc;
                }

                /* Save the IDL of pages freed by this txn, to a single record */
                if (freecnt < txn->mt_free_pgs[0]) {
                        if (!freecnt) {
                                /* Make sure last page of freeDB is touched and on freelist */
                                key.mv_size = MDB_MAXKEYSIZE+1;
                                key.mv_data = NULL;
                                rc = mdb_page_search(&mc, &key, MDB_PS_MODIFY);
                                if (rc && rc != MDB_NOTFOUND)
                                        return rc;
                        }
                        free_pgs = txn->mt_free_pgs;
                        /* Write to last page of freeDB */
                        key.mv_size = sizeof(txn->mt_txnid);
                        key.mv_data = &txn->mt_txnid;
                        do {
                                freecnt = free_pgs[0];
                                data.mv_size = MDB_IDL_SIZEOF(free_pgs);
                                rc = mdb_cursor_put(&mc, &key, &data, MDB_RESERVE);
                                if (rc)
                                        return rc;
                                /* Retry if mt_free_pgs[] grew during the Put() */
                                free_pgs = txn->mt_free_pgs;
                        } while (freecnt < free_pgs[0]);
                        mdb_midl_sort(free_pgs);
                        memcpy(data.mv_data, free_pgs, data.mv_size);
#if MDB_DEBUG > 1
                        {
                                unsigned int i = free_pgs[0];
                                DPRINTF("IDL write txn %zu root %zu num %u",
                                        txn->mt_txnid, txn->mt_dbs[FREE_DBI].md_root, i);
                                for (; i; i--)
                                        DPRINTF("IDL %zu", free_pgs[i]);
                        }
#endif
                        continue;
                }

                mop = env->me_pghead;
                mop_len = mop ? mop[0] : 0;

                /* Reserve records for me_pghead[]. Split it if multi-page,
                 * to avoid searching freeDB for a page range. Use keys in
                 * range [1,me_pglast]: Smaller than txnid of oldest reader.
                 */
                if (total_room >= mop_len) {
                        if (total_room == mop_len || --more < 0)
                                break;
                } else if (head_room >= maxfree_1pg && head_id > 1) {
                        /* Keep current record (overflow page), add a new one */
                        head_id--;
                        head_room = 0;
                }
                /* (Re)write {key = head_id, IDL length = head_room} */
                total_room -= head_room;
                head_room = mop_len - total_room;
                if (head_room > maxfree_1pg && head_id > 1) {
                        /* Overflow multi-page for part of me_pghead */
                        head_room /= head_id; /* amortize page sizes */
                        head_room += maxfree_1pg - head_room % (maxfree_1pg + 1);
                } else if (head_room < 0) {
                        /* Rare case, not bothering to delete this record */
                        head_room = 0;
                }
                key.mv_size = sizeof(head_id);
                key.mv_data = &head_id;
                data.mv_size = (head_room + 1) * sizeof(pgno_t);
                rc = mdb_cursor_put(&mc, &key, &data, MDB_RESERVE);
                if (rc)
                        return rc;
                *(MDB_ID *)data.mv_data = 0; /* IDL is initially empty */
                total_room += head_room;
        }

        /* Fill in the reserved, touched me_pghead records */
        rc = MDB_SUCCESS;
        if (mop_len) {
                MDB_val key, data;

                mop += mop_len;
                rc = mdb_cursor_first(&mc, &key, &data);
                for (; !rc; rc = mdb_cursor_next(&mc, &key, &data, MDB_NEXT)) {
                        unsigned flags = MDB_CURRENT;
                        txnid_t id = *(txnid_t *)key.mv_data;
                        ssize_t len = (ssize_t)(data.mv_size / sizeof(MDB_ID)) - 1;
                        MDB_ID save;

                        assert(len >= 0 && id <= env->me_pglast);
                        key.mv_data = &id;
                        if (len > mop_len) {
                                len = mop_len;
                                data.mv_size = (len + 1) * sizeof(MDB_ID);
                                flags = 0;
                        }
                        data.mv_data = mop -= len;
                        save = mop[0];
                        mop[0] = len;
                        rc = mdb_cursor_put(&mc, &key, &data, flags);
                        mop[0] = save;
                        if (rc || !(mop_len -= len))
                                break;
                }
        }
        return rc;
}

/** Flush dirty pages to the map, after clearing their dirty flag.
 */
static int
mdb_page_flush(MDB_txn *txn)
{
        MDB_env         *env = txn->mt_env;
        MDB_ID2L        dl = txn->mt_u.dirty_list;
        unsigned        psize = env->me_psize, j;
        int                     i, pagecount = dl[0].mid, rc;
        size_t          size = 0, pos = 0;
        pgno_t          pgno = 0;
        MDB_page        *dp = NULL;
#ifdef _WIN32
        OVERLAPPED      ov;
#else
        struct iovec iov[MDB_COMMIT_PAGES];
        ssize_t         wpos = 0, wsize = 0, wres;
        size_t          next_pos = 1; /* impossible pos, so pos != next_pos */
        int                     n = 0;
#endif

        j = 0;
        if (env->me_flags & MDB_WRITEMAP) {
                /* Clear dirty flags */
                for (i = pagecount; i; i--) {
                        dp = dl[i].mptr;
                        /* Don't flush this page yet */
                        if (dp->mp_flags & P_KEEP) {
                                dp->mp_flags ^= P_KEEP;
                                dl[++j] = dl[i];
                                continue;
                        }
                        dp->mp_flags &= ~P_DIRTY;
                }
                dl[0].mid = j;
                return MDB_SUCCESS;
        }

        /* Write the pages */
        for (i = 1;; i++) {
                if (i <= pagecount) {
                        dp = dl[i].mptr;
                        /* Don't flush this page yet */
                        if (dp->mp_flags & P_KEEP) {
                                dp->mp_flags ^= P_KEEP;
                                dl[i].mid = 0;
                                continue;
                        }
                        pgno = dl[i].mid;
                        /* clear dirty flag */
                        dp->mp_flags &= ~P_DIRTY;
                        pos = pgno * psize;
                        size = psize;
                        if (IS_OVERFLOW(dp)) size *= dp->mp_pages;
                }
#ifdef _WIN32
                else break;

                /* Windows actually supports scatter/gather I/O, but only on
                 * unbuffered file handles. Since we're relying on the OS page
                 * cache for all our data, that's self-defeating. So we just
                 * write pages one at a time. We use the ov structure to set
                 * the write offset, to at least save the overhead of a Seek
                 * system call.
                 */
                DPRINTF("committing page %zu", pgno);
                memset(&ov, 0, sizeof(ov));
                ov.Offset = pos & 0xffffffff;
                ov.OffsetHigh = pos >> 16 >> 16;
                if (!WriteFile(env->me_fd, dp, size, NULL, &ov)) {
                        rc = ErrCode();
                        DPRINTF("WriteFile: %d", rc);
                        return rc;
                }
#else
                /* Write up to MDB_COMMIT_PAGES dirty pages at a time. */
                if (pos!=next_pos || n==MDB_COMMIT_PAGES || wsize+size>MAX_WRITE) {
                        if (n) {
                                /* Write previous page(s) */
#ifdef MDB_USE_PWRITEV
                                wres = pwritev(env->me_fd, iov, n, wpos);
#else
                                if (n == 1) {
                                        wres = pwrite(env->me_fd, iov[0].iov_base, wsize, wpos);
                                } else {
                                        if (lseek(env->me_fd, wpos, SEEK_SET) == -1) {
                                                rc = ErrCode();
                                                DPRINTF("lseek: %s", strerror(rc));
                                                return rc;
                                        }
                                        wres = writev(env->me_fd, iov, n);
                                }
#endif
                                if (wres != wsize) {
                                        if (wres < 0) {
                                                rc = ErrCode();
                                                DPRINTF("Write error: %s", strerror(rc));
                                        } else {
                                                rc = EIO; /* TODO: Use which error code? */
                                                DPUTS("short write, filesystem full?");
                                        }
                                        return rc;
                                }
                                n = 0;
                        }
                        if (i > pagecount)
                                break;
                        wpos = pos;
                        wsize = 0;
                }
                DPRINTF("committing page %zu", pgno);
                next_pos = pos + size;
                iov[n].iov_len = size;
                iov[n].iov_base = (char *)dp;
                wsize += size;
                n++;
#endif  /* _WIN32 */
        }

        j = 0;
        for (i=1; i<=pagecount; i++) {
                dp = dl[i].mptr;
                /* This is a page we skipped above */
                if (!dl[i].mid) {
                        dl[++j] = dl[i];
                        dl[j].mid = dp->mp_pgno;
                        continue;
                }
                mdb_dpage_free(env, dp);
        }
        dl[0].mid = j;

        return MDB_SUCCESS;
}

int
mdb_txn_commit(MDB_txn *txn)
{
        int             rc;
        unsigned int i;
        MDB_env *env;

        assert(txn != NULL);
        assert(txn->mt_env != NULL);

        if (txn->mt_child) {
                rc = mdb_txn_commit(txn->mt_child);
                txn->mt_child = NULL;
                if (rc)
                        goto fail;
        }

        env = txn->mt_env;

        if (F_ISSET(txn->mt_flags, MDB_TXN_RDONLY)) {
                mdb_dbis_update(txn, 1);
                txn->mt_numdbs = 2; /* so txn_abort() doesn't close any new handles */
                mdb_txn_abort(txn);
                return MDB_SUCCESS;
        }

        if (F_ISSET(txn->mt_flags, MDB_TXN_ERROR)) {
                DPUTS("error flag is set, can't commit");
                if (txn->mt_parent)
                        txn->mt_parent->mt_flags |= MDB_TXN_ERROR;
                rc = EINVAL;
                goto fail;
        }

        if (txn->mt_parent) {
                MDB_txn *parent = txn->mt_parent;
                unsigned x, y, len;
                MDB_ID2L dst, src;

                /* Append our free list to parent's */
                rc = mdb_midl_append_list(&parent->mt_free_pgs, txn->mt_free_pgs);
                if (rc)
                        goto fail;
                mdb_midl_free(txn->mt_free_pgs);

                parent->mt_next_pgno = txn->mt_next_pgno;
                parent->mt_flags = txn->mt_flags;

                /* Merge our cursors into parent's and close them */
                mdb_cursors_close(txn, 1);

                /* Update parent's DB table. */
                memcpy(parent->mt_dbs, txn->mt_dbs, txn->mt_numdbs * sizeof(MDB_db));
                parent->mt_numdbs = txn->mt_numdbs;
                parent->mt_dbflags[0] = txn->mt_dbflags[0];
                parent->mt_dbflags[1] = txn->mt_dbflags[1];
                for (i=2; i<txn->mt_numdbs; i++) {
                        /* preserve parent's DB_NEW status */
                        x = parent->mt_dbflags[i] & DB_NEW;
                        parent->mt_dbflags[i] = txn->mt_dbflags[i] | x;
                }

                dst = parent->mt_u.dirty_list;
                src = txn->mt_u.dirty_list;
                /* Remove anything in our dirty list from parent's spill list */
                if (parent->mt_spill_pgs) {
                        x = parent->mt_spill_pgs[0];
                        len = x;
                        /* zero out our dirty pages in parent spill list */
                        for (i=1; i<=src[0].mid; i++) {
                                if (src[i].mid < parent->mt_spill_pgs[x])
                                        continue;
                                if (src[i].mid > parent->mt_spill_pgs[x]) {
                                        if (x <= 1)
                                                break;
                                        x--;
                                        continue;
                                }
                                parent->mt_spill_pgs[x] = 0;
                                len--;
                        }
                        /* OK, we had a few hits, squash zeros from the spill list */
                        if (len < parent->mt_spill_pgs[0]) {
                                x=1;
                                for (y=1; y<=parent->mt_spill_pgs[0]; y++) {
                                        if (parent->mt_spill_pgs[y]) {
                                                if (y != x) {
                                                        parent->mt_spill_pgs[x] = parent->mt_spill_pgs[y];
                                                }
                                                x++;
                                        }
                                }
                                parent->mt_spill_pgs[0] = len;
                        }
                }
                /* Find len = length of merging our dirty list with parent's */
                x = dst[0].mid;
                dst[0].mid = 0;         /* simplify loops */
                if (parent->mt_parent) {
                        len = x + src[0].mid;
                        y = mdb_mid2l_search(src, dst[x].mid + 1) - 1;
                        for (i = x; y && i; y--) {
                                pgno_t yp = src[y].mid;
                                while (yp < dst[i].mid)
                                        i--;
                                if (yp == dst[i].mid) {
                                        i--;
                                        len--;
                                }
                        }
                } else { /* Simplify the above for single-ancestor case */
                        len = MDB_IDL_UM_MAX - txn->mt_dirty_room;
                }
                /* Merge our dirty list with parent's */
                y = src[0].mid;
                for (i = len; y; dst[i--] = src[y--]) {
                        pgno_t yp = src[y].mid;
                        while (yp < dst[x].mid)
                                dst[i--] = dst[x--];
                        if (yp == dst[x].mid)
                                free(dst[x--].mptr);
                }
                assert(i == x);
                dst[0].mid = len;
                free(txn->mt_u.dirty_list);
                parent->mt_dirty_room = txn->mt_dirty_room;
                if (txn->mt_spill_pgs) {
                        if (parent->mt_spill_pgs) {
                                mdb_midl_append_list(&parent->mt_spill_pgs, txn->mt_spill_pgs);
                                mdb_midl_free(txn->mt_spill_pgs);
                                mdb_midl_sort(parent->mt_spill_pgs);
                        } else {
                                parent->mt_spill_pgs = txn->mt_spill_pgs;
                        }
                }

                parent->mt_child = NULL;
                mdb_midl_free(((MDB_ntxn *)txn)->mnt_pgstate.mf_pghead);
                free(txn);
                return MDB_SUCCESS;
        }

        if (txn != env->me_txn) {
                DPUTS("attempt to commit unknown transaction");
                rc = EINVAL;
                goto fail;
        }

        mdb_cursors_close(txn, 0);

        if (!txn->mt_u.dirty_list[0].mid && !(txn->mt_flags & MDB_TXN_DIRTY))
                goto done;

        DPRINTF("committing txn %zu %p on mdbenv %p, root page %zu",
            txn->mt_txnid, (void *)txn, (void *)env, txn->mt_dbs[MAIN_DBI].md_root);

        /* Update DB root pointers */
        if (txn->mt_numdbs > 2) {
                MDB_cursor mc;
                MDB_dbi i;
                MDB_val data;
                data.mv_size = sizeof(MDB_db);

                mdb_cursor_init(&mc, txn, MAIN_DBI, NULL);
                for (i = 2; i < txn->mt_numdbs; i++) {
                        if (txn->mt_dbflags[i] & DB_DIRTY) {
                                data.mv_data = &txn->mt_dbs[i];
                                rc = mdb_cursor_put(&mc, &txn->mt_dbxs[i].md_name, &data, 0);
                                if (rc)
                                        goto fail;
                        }
                }
        }

        rc = mdb_freelist_save(txn);
        if (rc)
                goto fail;

        mdb_midl_free(env->me_pghead);
        env->me_pghead = NULL;
        if (mdb_midl_shrink(&txn->mt_free_pgs))
                env->me_free_pgs = txn->mt_free_pgs;

#if MDB_DEBUG > 2
        mdb_audit(txn);
#endif

        if ((rc = mdb_page_flush(txn)) ||
                (rc = mdb_env_sync(env, 0)) ||
                (rc = mdb_env_write_meta(txn)))
                goto fail;

done:
        env->me_pglast = 0;
        env->me_txn = NULL;
        mdb_dbis_update(txn, 1);

        UNLOCK_MUTEX_W(env);
        free(txn);

        return MDB_SUCCESS;

fail:
        mdb_txn_abort(txn);
        return rc;
}

/** Read the environment parameters of a DB environment before
 * mapping it into memory.
 * @param[in] env the environment handle
 * @param[out] meta address of where to store the meta information
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_env_read_header(MDB_env *env, MDB_meta *meta)
{
        MDB_pagebuf     pbuf;
        MDB_page        *p;
        MDB_meta        *m;
        int                     i, rc, off;

        /* We don't know the page size yet, so use a minimum value.
         * Read both meta pages so we can use the latest one.
         */

        for (i=off=0; i<2; i++, off = meta->mm_psize) {
#ifdef _WIN32
                DWORD len;
                OVERLAPPED ov;
                memset(&ov, 0, sizeof(ov));
                ov.Offset = off;
                rc = ReadFile(env->me_fd,&pbuf,MDB_PAGESIZE,&len,&ov) ? (int)len : -1;
                if (rc == -1 && ErrCode() == ERROR_HANDLE_EOF)
                        rc = 0;
#else
                rc = pread(env->me_fd, &pbuf, MDB_PAGESIZE, off);
#endif
                if (rc != MDB_PAGESIZE) {
                        if (rc == 0 && off == 0)
                                return ENOENT;
                        rc = rc < 0 ? (int) ErrCode() : MDB_INVALID;
                        DPRINTF("read: %s", mdb_strerror(rc));
                        return rc;
                }

                p = (MDB_page *)&pbuf;

                if (!F_ISSET(p->mp_flags, P_META)) {
                        DPRINTF("page %zu not a meta page", p->mp_pgno);
                        return MDB_INVALID;
                }

                m = METADATA(p);
                if (m->mm_magic != MDB_MAGIC) {
                        DPUTS("meta has invalid magic");
                        return MDB_INVALID;
                }

                if (m->mm_version != MDB_VERSION) {
                        DPRINTF("database is version %u, expected version %u",
                                m->mm_version, MDB_VERSION);
                        return MDB_VERSION_MISMATCH;
                }

                if (off == 0 || m->mm_txnid > meta->mm_txnid)
                        *meta = *m;
        }
        return 0;
}

/** Write the environment parameters of a freshly created DB environment.
 * @param[in] env the environment handle
 * @param[out] meta address of where to store the meta information
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_env_init_meta(MDB_env *env, MDB_meta *meta)
{
        MDB_page *p, *q;
        int rc;
        unsigned int     psize;

        DPUTS("writing new meta page");

        GET_PAGESIZE(psize);

        meta->mm_magic = MDB_MAGIC;
        meta->mm_version = MDB_VERSION;
        meta->mm_mapsize = env->me_mapsize;
        meta->mm_psize = psize;
        meta->mm_last_pg = 1;
        meta->mm_flags = env->me_flags & 0xffff;
        meta->mm_flags |= MDB_INTEGERKEY;
        meta->mm_dbs[0].md_root = P_INVALID;
        meta->mm_dbs[1].md_root = P_INVALID;

        p = calloc(2, psize);
        p->mp_pgno = 0;
        p->mp_flags = P_META;
        *(MDB_meta *)METADATA(p) = *meta;

        q = (MDB_page *)((char *)p + psize);
        q->mp_pgno = 1;
        q->mp_flags = P_META;
        *(MDB_meta *)METADATA(q) = *meta;

#ifdef _WIN32
        {
                DWORD len;
                OVERLAPPED ov;
                memset(&ov, 0, sizeof(ov));
                rc = WriteFile(env->me_fd, p, psize * 2, &len, &ov);
                rc = rc ? (len == psize * 2 ? MDB_SUCCESS : EIO) : ErrCode();
        }
#else
        rc = pwrite(env->me_fd, p, psize * 2, 0);
        rc = (rc == (int)psize * 2) ? MDB_SUCCESS : rc < 0 ? ErrCode() : EIO;
#endif
        free(p);
        return rc;
}

/** Update the environment info to commit a transaction.
 * @param[in] txn the transaction that's being committed
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_env_write_meta(MDB_txn *txn)
{
        MDB_env *env;
        MDB_meta        meta, metab, *mp;
        off_t off;
        int rc, len, toggle;
        char *ptr;
        HANDLE mfd;
#ifdef _WIN32
        OVERLAPPED ov;
#else
        int r2;
#endif

        assert(txn != NULL);
        assert(txn->mt_env != NULL);

        toggle = !txn->mt_toggle;
        DPRINTF("writing meta page %d for root page %zu",
                toggle, txn->mt_dbs[MAIN_DBI].md_root);

        env = txn->mt_env;
        mp = env->me_metas[toggle];

        if (env->me_flags & MDB_WRITEMAP) {
                /* Persist any increases of mapsize config */
                if (env->me_mapsize > mp->mm_mapsize)
                        mp->mm_mapsize = env->me_mapsize;
                mp->mm_dbs[0] = txn->mt_dbs[0];
                mp->mm_dbs[1] = txn->mt_dbs[1];
                mp->mm_last_pg = txn->mt_next_pgno - 1;
                mp->mm_txnid = txn->mt_txnid;
                if (!(env->me_flags & (MDB_NOMETASYNC|MDB_NOSYNC))) {
                        rc = (env->me_flags & MDB_MAPASYNC) ? MS_ASYNC : MS_SYNC;
                        ptr = env->me_map;
                        if (toggle)
                                ptr += env->me_psize;
                        if (MDB_MSYNC(ptr, env->me_psize, rc)) {
                                rc = ErrCode();
                                goto fail;
                        }
                }
                goto done;
        }
        metab.mm_txnid = env->me_metas[toggle]->mm_txnid;
        metab.mm_last_pg = env->me_metas[toggle]->mm_last_pg;

        ptr = (char *)&meta;
        if (env->me_mapsize > mp->mm_mapsize) {
                /* Persist any increases of mapsize config */
                meta.mm_mapsize = env->me_mapsize;
                off = offsetof(MDB_meta, mm_mapsize);
        } else {
                off = offsetof(MDB_meta, mm_dbs[0].md_depth);
        }
        len = sizeof(MDB_meta) - off;

        ptr += off;
        meta.mm_dbs[0] = txn->mt_dbs[0];
        meta.mm_dbs[1] = txn->mt_dbs[1];
        meta.mm_last_pg = txn->mt_next_pgno - 1;
        meta.mm_txnid = txn->mt_txnid;

        if (toggle)
                off += env->me_psize;
        off += PAGEHDRSZ;

        /* Write to the SYNC fd */
        mfd = env->me_flags & (MDB_NOSYNC|MDB_NOMETASYNC) ?
                env->me_fd : env->me_mfd;
#ifdef _WIN32
        {
                memset(&ov, 0, sizeof(ov));
                ov.Offset = off;
                if (!WriteFile(mfd, ptr, len, (DWORD *)&rc, &ov))
                        rc = -1;
        }
#else
        rc = pwrite(mfd, ptr, len, off);
#endif
        if (rc != len) {
                rc = rc < 0 ? ErrCode() : EIO;
                DPUTS("write failed, disk error?");
                /* On a failure, the pagecache still contains the new data.
                 * Write some old data back, to prevent it from being used.
                 * Use the non-SYNC fd; we know it will fail anyway.
                 */
                meta.mm_last_pg = metab.mm_last_pg;
                meta.mm_txnid = metab.mm_txnid;
#ifdef _WIN32
                memset(&ov, 0, sizeof(ov));
                ov.Offset = off;
                WriteFile(env->me_fd, ptr, len, NULL, &ov);
#else
                r2 = pwrite(env->me_fd, ptr, len, off);
#endif
fail:
                env->me_flags |= MDB_FATAL_ERROR;
                return rc;
        }
done:
        /* Memory ordering issues are irrelevant; since the entire writer
         * is wrapped by wmutex, all of these changes will become visible
         * after the wmutex is unlocked. Since the DB is multi-version,
         * readers will get consistent data regardless of how fresh or
         * how stale their view of these values is.
         */
        env->me_txns->mti_txnid = txn->mt_txnid;

        return MDB_SUCCESS;
}

/** Check both meta pages to see which one is newer.
 * @param[in] env the environment handle
 * @return meta toggle (0 or 1).
 */
static int
mdb_env_pick_meta(const MDB_env *env)
{
        return (env->me_metas[0]->mm_txnid < env->me_metas[1]->mm_txnid);
}

int
mdb_env_create(MDB_env **env)
{
        MDB_env *e;

        e = calloc(1, sizeof(MDB_env));
        if (!e)
                return ENOMEM;

        e->me_maxreaders = DEFAULT_READERS;
        e->me_maxdbs = e->me_numdbs = 2;
        e->me_fd = INVALID_HANDLE_VALUE;
        e->me_lfd = INVALID_HANDLE_VALUE;
        e->me_mfd = INVALID_HANDLE_VALUE;
#ifdef MDB_USE_POSIX_SEM
        e->me_rmutex = SEM_FAILED;
        e->me_wmutex = SEM_FAILED;
#endif
        e->me_pid = getpid();
        VGMEMP_CREATE(e,0,0);
        *env = e;
        return MDB_SUCCESS;
}

int
mdb_env_set_mapsize(MDB_env *env, size_t size)
{
        if (env->me_map)
                return EINVAL;
        env->me_mapsize = size;
        if (env->me_psize)
                env->me_maxpg = env->me_mapsize / env->me_psize;
        return MDB_SUCCESS;
}

int
mdb_env_set_maxdbs(MDB_env *env, MDB_dbi dbs)
{
        if (env->me_map)
                return EINVAL;
        env->me_maxdbs = dbs + 2; /* Named databases + main and free DB */
        return MDB_SUCCESS;
}

int
mdb_env_set_maxreaders(MDB_env *env, unsigned int readers)
{
        if (env->me_map || readers < 1)
                return EINVAL;
        env->me_maxreaders = readers;
        return MDB_SUCCESS;
}

int
mdb_env_get_maxreaders(MDB_env *env, unsigned int *readers)
{
        if (!env || !readers)
                return EINVAL;
        *readers = env->me_maxreaders;
        return MDB_SUCCESS;
}

/** Further setup required for opening an MDB environment
 */
static int
mdb_env_open2(MDB_env *env)
{
        unsigned int flags = env->me_flags;
        int i, newenv = 0;
        MDB_meta meta;
        MDB_page *p;
#ifndef _WIN32
        int prot;
#endif

        memset(&meta, 0, sizeof(meta));

        if ((i = mdb_env_read_header(env, &meta)) != 0) {
                if (i != ENOENT)
                        return i;
                DPUTS("new mdbenv");
                newenv = 1;
        }

        /* Was a mapsize configured? */
        if (!env->me_mapsize) {
                /* If this is a new environment, take the default,
                 * else use the size recorded in the existing env.
                 */
                env->me_mapsize = newenv ? DEFAULT_MAPSIZE : meta.mm_mapsize;
        } else if (env->me_mapsize < meta.mm_mapsize) {
                /* If the configured size is smaller, make sure it's
                 * still big enough. Silently round up to minimum if not.
                 */
                size_t minsize = (meta.mm_last_pg + 1) * meta.mm_psize;
                if (env->me_mapsize < minsize)
                        env->me_mapsize = minsize;
        }

#ifdef _WIN32
        {
                int rc;
                HANDLE mh;
                LONG sizelo, sizehi;
                sizelo = env->me_mapsize & 0xffffffff;
                sizehi = env->me_mapsize >> 16 >> 16; /* only needed on Win64 */
                /* Windows won't create mappings for zero length files.
                 * Just allocate the maxsize right now.
                 */
                if (newenv) {
                        if (SetFilePointer(env->me_fd, sizelo, &sizehi, 0) != (DWORD)sizelo
                                || !SetEndOfFile(env->me_fd)
                                || SetFilePointer(env->me_fd, 0, NULL, 0) != 0)
                                return ErrCode();
                }
                mh = CreateFileMapping(env->me_fd, NULL, flags & MDB_WRITEMAP ?
                        PAGE_READWRITE : PAGE_READONLY,
                        sizehi, sizelo, NULL);
                if (!mh)
                        return ErrCode();
                env->me_map = MapViewOfFileEx(mh, flags & MDB_WRITEMAP ?
                        FILE_MAP_WRITE : FILE_MAP_READ,
                        0, 0, env->me_mapsize, meta.mm_address);
                rc = env->me_map ? 0 : ErrCode();
                CloseHandle(mh);
                if (rc)
                        return rc;
        }
#else
        i = MAP_SHARED;
        prot = PROT_READ;
        if (flags & MDB_WRITEMAP) {
                prot |= PROT_WRITE;
                if (ftruncate(env->me_fd, env->me_mapsize) < 0)
                        return ErrCode();
        }
        env->me_map = mmap(meta.mm_address, env->me_mapsize, prot, i,
                env->me_fd, 0);
        if (env->me_map == MAP_FAILED) {
                env->me_map = NULL;
                return ErrCode();
        }
        /* Turn off readahead. It's harmful when the DB is larger than RAM. */
#ifdef MADV_RANDOM
        madvise(env->me_map, env->me_mapsize, MADV_RANDOM);
#else
#ifdef POSIX_MADV_RANDOM
        posix_madvise(env->me_map, env->me_mapsize, POSIX_MADV_RANDOM);
#endif /* POSIX_MADV_RANDOM */
#endif /* MADV_RANDOM */
#endif /* _WIN32 */

        if (newenv) {
                if (flags & MDB_FIXEDMAP)
                        meta.mm_address = env->me_map;
                i = mdb_env_init_meta(env, &meta);
                if (i != MDB_SUCCESS) {
                        return i;
                }
        } else if (meta.mm_address && env->me_map != meta.mm_address) {
                /* Can happen because the address argument to mmap() is just a
                 * hint.  mmap() can pick another, e.g. if the range is in use.
                 * The MAP_FIXED flag would prevent that, but then mmap could
                 * instead unmap existing pages to make room for the new map.
                 */
                return EBUSY;   /* TODO: Make a new MDB_* error code? */
        }
        env->me_psize = meta.mm_psize;
        env->me_maxfree_1pg = (env->me_psize - PAGEHDRSZ) / sizeof(pgno_t) - 1;
        env->me_nodemax = (env->me_psize - PAGEHDRSZ) / MDB_MINKEYS;

        env->me_maxpg = env->me_mapsize / env->me_psize;

        p = (MDB_page *)env->me_map;
        env->me_metas[0] = METADATA(p);
        env->me_metas[1] = (MDB_meta *)((char *)env->me_metas[0] + meta.mm_psize);

#if MDB_DEBUG
        {
                int toggle = mdb_env_pick_meta(env);
                MDB_db *db = &env->me_metas[toggle]->mm_dbs[MAIN_DBI];

                DPRINTF("opened database version %u, pagesize %u",
                        env->me_metas[0]->mm_version, env->me_psize);
                DPRINTF("using meta page %d",  toggle);
                DPRINTF("depth: %u",           db->md_depth);
                DPRINTF("entries: %zu",        db->md_entries);
                DPRINTF("branch pages: %zu",   db->md_branch_pages);
                DPRINTF("leaf pages: %zu",     db->md_leaf_pages);
                DPRINTF("overflow pages: %zu", db->md_overflow_pages);
                DPRINTF("root: %zu",           db->md_root);
        }
#endif

        return MDB_SUCCESS;
}


/** Release a reader thread's slot in the reader lock table.
 *      This function is called automatically when a thread exits.
 * @param[in] ptr This points to the slot in the reader lock table.
 */
static void
mdb_env_reader_dest(void *ptr)
{
        MDB_reader *reader = ptr;

        reader->mr_pid = 0;
}

#ifdef _WIN32
/** Junk for arranging thread-specific callbacks on Windows. This is
 *      necessarily platform and compiler-specific. Windows supports up
 *      to 1088 keys. Let's assume nobody opens more than 64 environments
 *      in a single process, for now. They can override this if needed.
 */
#ifndef MAX_TLS_KEYS
#define MAX_TLS_KEYS    64
#endif
static pthread_key_t mdb_tls_keys[MAX_TLS_KEYS];
static int mdb_tls_nkeys;

static void NTAPI mdb_tls_callback(PVOID module, DWORD reason, PVOID ptr)
{
        int i;
        switch(reason) {
        case DLL_PROCESS_ATTACH: break;
        case DLL_THREAD_ATTACH: break;
        case DLL_THREAD_DETACH:
                for (i=0; i<mdb_tls_nkeys; i++) {
                        MDB_reader *r = pthread_getspecific(mdb_tls_keys[i]);
                        mdb_env_reader_dest(r);
                }
                break;
        case DLL_PROCESS_DETACH: break;
        }
}
#ifdef __GNUC__
#ifdef _WIN64
const PIMAGE_TLS_CALLBACK mdb_tls_cbp __attribute__((section (".CRT$XLB"))) = mdb_tls_callback;
#else
PIMAGE_TLS_CALLBACK mdb_tls_cbp __attribute__((section (".CRT$XLB"))) = mdb_tls_callback;
#endif
#else
#ifdef _WIN64
/* Force some symbol references.
 *      _tls_used forces the linker to create the TLS directory if not already done
 *      mdb_tls_cbp prevents whole-program-optimizer from dropping the symbol.
 */
#pragma comment(linker, "/INCLUDE:_tls_used")
#pragma comment(linker, "/INCLUDE:mdb_tls_cbp")
#pragma const_seg(".CRT$XLB")
extern const PIMAGE_TLS_CALLBACK mdb_tls_callback;
const PIMAGE_TLS_CALLBACK mdb_tls_cbp = mdb_tls_callback;
#pragma const_seg()
#else   /* WIN32 */
#pragma comment(linker, "/INCLUDE:__tls_used")
#pragma comment(linker, "/INCLUDE:_mdb_tls_cbp")
#pragma data_seg(".CRT$XLB")
PIMAGE_TLS_CALLBACK mdb_tls_cbp = mdb_tls_callback;
#pragma data_seg()
#endif  /* WIN 32/64 */
#endif  /* !__GNUC__ */
#endif

/** Downgrade the exclusive lock on the region back to shared */
static int
mdb_env_share_locks(MDB_env *env, int *excl)
{
        int rc = 0, toggle = mdb_env_pick_meta(env);

        env->me_txns->mti_txnid = env->me_metas[toggle]->mm_txnid;

#ifdef _WIN32
        {
                OVERLAPPED ov;
                /* First acquire a shared lock. The Unlock will
                 * then release the existing exclusive lock.
                 */
                memset(&ov, 0, sizeof(ov));
                if (!LockFileEx(env->me_lfd, 0, 0, 1, 0, &ov)) {
                        rc = ErrCode();
                } else {
                        UnlockFile(env->me_lfd, 0, 0, 1, 0);
                        *excl = 0;
                }
        }
#else
        {
                struct flock lock_info;
                /* The shared lock replaces the existing lock */
                memset((void *)&lock_info, 0, sizeof(lock_info));
                lock_info.l_type = F_RDLCK;
                lock_info.l_whence = SEEK_SET;
                lock_info.l_start = 0;
                lock_info.l_len = 1;
                while ((rc = fcntl(env->me_lfd, F_SETLK, &lock_info)) &&
                                (rc = ErrCode()) == EINTR) ;
                *excl = rc ? -1 : 0;    /* error may mean we lost the lock */
        }
#endif

        return rc;
}

/** Try to get exlusive lock, otherwise shared.
 *      Maintain *excl = -1: no/unknown lock, 0: shared, 1: exclusive.
 */
static int
mdb_env_excl_lock(MDB_env *env, int *excl)
{
        int rc = 0;
#ifdef _WIN32
        if (LockFile(env->me_lfd, 0, 0, 1, 0)) {
                *excl = 1;
        } else {
                OVERLAPPED ov;
                memset(&ov, 0, sizeof(ov));
                if (LockFileEx(env->me_lfd, 0, 0, 1, 0, &ov)) {
                        *excl = 0;
                } else {
                        rc = ErrCode();
                }
        }
#else
        struct flock lock_info;
        memset((void *)&lock_info, 0, sizeof(lock_info));
        lock_info.l_type = F_WRLCK;
        lock_info.l_whence = SEEK_SET;
        lock_info.l_start = 0;
        lock_info.l_len = 1;
        while ((rc = fcntl(env->me_lfd, F_SETLK, &lock_info)) &&
                        (rc = ErrCode()) == EINTR) ;
        if (!rc) {
                *excl = 1;
        } else
# ifdef MDB_USE_POSIX_SEM
        if (*excl < 0) /* always true when !MDB_USE_POSIX_SEM */
# endif
        {
                lock_info.l_type = F_RDLCK;
                while ((rc = fcntl(env->me_lfd, F_SETLKW, &lock_info)) &&
                                (rc = ErrCode()) == EINTR) ;
                if (rc == 0)
                        *excl = 0;
        }
#endif
        return rc;
}

#if defined(_WIN32) || defined(MDB_USE_POSIX_SEM)
/*
 * hash_64 - 64 bit Fowler/Noll/Vo-0 FNV-1a hash code
 *
 * @(#) $Revision: 5.1 $
 * @(#) $Id: hash_64a.c,v 5.1 2009/06/30 09:01:38 chongo Exp $
 * @(#) $Source: /usr/local/src/cmd/fnv/RCS/hash_64a.c,v $
 *
 *        http://www.isthe.com/chongo/tech/comp/fnv/index.html
 *
 ***
 *
 * Please do not copyright this code.  This code is in the public domain.
 *
 * LANDON CURT NOLL DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
 * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO
 * EVENT SHALL LANDON CURT NOLL BE LIABLE FOR ANY SPECIAL, INDIRECT OR
 * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF
 * USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
 * OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
 * PERFORMANCE OF THIS SOFTWARE.
 *
 * By:
 *      chongo <Landon Curt Noll> /\oo/\
 *        http://www.isthe.com/chongo/
 *
 * Share and Enjoy!     :-)
 */

typedef unsigned long long      mdb_hash_t;
#define MDB_HASH_INIT ((mdb_hash_t)0xcbf29ce484222325ULL)

/** perform a 64 bit Fowler/Noll/Vo FNV-1a hash on a buffer
 * @param[in] str string to hash
 * @param[in] hval      initial value for hash
 * @return 64 bit hash
 *
 * NOTE: To use the recommended 64 bit FNV-1a hash, use MDB_HASH_INIT as the
 *       hval arg on the first call.
 */
static mdb_hash_t
mdb_hash_val(MDB_val *val, mdb_hash_t hval)
{
        unsigned char *s = (unsigned char *)val->mv_data;       /* unsigned string */
        unsigned char *end = s + val->mv_size;
        /*
         * FNV-1a hash each octet of the string
         */
        while (s < end) {
                /* xor the bottom with the current octet */
                hval ^= (mdb_hash_t)*s++;

                /* multiply by the 64 bit FNV magic prime mod 2^64 */
                hval += (hval << 1) + (hval << 4) + (hval << 5) +
                        (hval << 7) + (hval << 8) + (hval << 40);
        }
        /* return our new hash value */
        return hval;
}

/** Hash the string and output the hash in hex.
 * @param[in] str string to hash
 * @param[out] hexbuf an array of 17 chars to hold the hash
 */
static void
mdb_hash_hex(MDB_val *val, char *hexbuf)
{
        int i;
        mdb_hash_t h = mdb_hash_val(val, MDB_HASH_INIT);
        for (i=0; i<8; i++) {
                hexbuf += sprintf(hexbuf, "%02x", (unsigned int)h & 0xff);
                h >>= 8;
        }
}
#endif

/** Open and/or initialize the lock region for the environment.
 * @param[in] env The MDB environment.
 * @param[in] lpath The pathname of the file used for the lock region.
 * @param[in] mode The Unix permissions for the file, if we create it.
 * @param[out] excl Resulting file lock type: -1 none, 0 shared, 1 exclusive
 * @param[in,out] excl In -1, out lock type: -1 none, 0 shared, 1 exclusive
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_env_setup_locks(MDB_env *env, char *lpath, int mode, int *excl)
{
#ifdef _WIN32
#       define MDB_ERRCODE_ROFS ERROR_WRITE_PROTECT
#else
#       define MDB_ERRCODE_ROFS EROFS
#ifdef O_CLOEXEC        /* Linux: Open file and set FD_CLOEXEC atomically */
#       define MDB_CLOEXEC              O_CLOEXEC
#else
        int fdflags;
#       define MDB_CLOEXEC              0
#endif
#endif
        int rc;
        off_t size, rsize;

#ifdef _WIN32
        env->me_lfd = CreateFile(lpath, GENERIC_READ|GENERIC_WRITE,
                FILE_SHARE_READ|FILE_SHARE_WRITE, NULL, OPEN_ALWAYS,
                FILE_ATTRIBUTE_NORMAL, NULL);
#else
        env->me_lfd = open(lpath, O_RDWR|O_CREAT|MDB_CLOEXEC, mode);
#endif
        if (env->me_lfd == INVALID_HANDLE_VALUE) {
                rc = ErrCode();
                if (rc == MDB_ERRCODE_ROFS && (env->me_flags & MDB_RDONLY)) {
                        return MDB_SUCCESS;
                }
                goto fail_errno;
        }
#if ! ((MDB_CLOEXEC) || defined(_WIN32))
        /* Lose record locks when exec*() */
        if ((fdflags = fcntl(env->me_lfd, F_GETFD) | FD_CLOEXEC) >= 0)
                        fcntl(env->me_lfd, F_SETFD, fdflags);
#endif

        if (!(env->me_flags & MDB_NOTLS)) {
                rc = pthread_key_create(&env->me_txkey, mdb_env_reader_dest);
                if (rc)
                        goto fail;
                env->me_flags |= MDB_ENV_TXKEY;
#ifdef _WIN32
                /* Windows TLS callbacks need help finding their TLS info. */
                if (mdb_tls_nkeys >= MAX_TLS_KEYS) {
                        rc = MDB_TLS_FULL;
                        goto fail;
                }
                mdb_tls_keys[mdb_tls_nkeys++] = env->me_txkey;
#endif
        }

        /* Try to get exclusive lock. If we succeed, then
         * nobody is using the lock region and we should initialize it.
         */
        if ((rc = mdb_env_excl_lock(env, excl))) goto fail;

#ifdef _WIN32
        size = GetFileSize(env->me_lfd, NULL);
#else
        size = lseek(env->me_lfd, 0, SEEK_END);
        if (size == -1) goto fail_errno;
#endif
        rsize = (env->me_maxreaders-1) * sizeof(MDB_reader) + sizeof(MDB_txninfo);
        if (size < rsize && *excl > 0) {
#ifdef _WIN32
                if (SetFilePointer(env->me_lfd, rsize, NULL, FILE_BEGIN) != rsize
                        || !SetEndOfFile(env->me_lfd))
                        goto fail_errno;
#else
                if (ftruncate(env->me_lfd, rsize) != 0) goto fail_errno;
#endif
        } else {
                rsize = size;
                size = rsize - sizeof(MDB_txninfo);
                env->me_maxreaders = size/sizeof(MDB_reader) + 1;
        }
        {
#ifdef _WIN32
                HANDLE mh;
                mh = CreateFileMapping(env->me_lfd, NULL, PAGE_READWRITE,
                        0, 0, NULL);
                if (!mh) goto fail_errno;
                env->me_txns = MapViewOfFileEx(mh, FILE_MAP_WRITE, 0, 0, rsize, NULL);
                CloseHandle(mh);
                if (!env->me_txns) goto fail_errno;
#else
                void *m = mmap(NULL, rsize, PROT_READ|PROT_WRITE, MAP_SHARED,
                        env->me_lfd, 0);
                if (m == MAP_FAILED) goto fail_errno;
                env->me_txns = m;
#endif
        }
        if (*excl > 0) {
#ifdef _WIN32
                BY_HANDLE_FILE_INFORMATION stbuf;
                struct {
                        DWORD volume;
                        DWORD nhigh;
                        DWORD nlow;
                } idbuf;
                MDB_val val;
                char hexbuf[17];

                if (!mdb_sec_inited) {
                        InitializeSecurityDescriptor(&mdb_null_sd,
                                SECURITY_DESCRIPTOR_REVISION);
                        SetSecurityDescriptorDacl(&mdb_null_sd, TRUE, 0, FALSE);
                        mdb_all_sa.nLength = sizeof(SECURITY_ATTRIBUTES);
                        mdb_all_sa.bInheritHandle = FALSE;
                        mdb_all_sa.lpSecurityDescriptor = &mdb_null_sd;
                        mdb_sec_inited = 1;
                }
                if (!GetFileInformationByHandle(env->me_lfd, &stbuf)) goto fail_errno;
                idbuf.volume = stbuf.dwVolumeSerialNumber;
                idbuf.nhigh  = stbuf.nFileIndexHigh;
                idbuf.nlow   = stbuf.nFileIndexLow;
                val.mv_data = &idbuf;
                val.mv_size = sizeof(idbuf);
                mdb_hash_hex(&val, hexbuf);
                sprintf(env->me_txns->mti_rmname, "Global\\MDBr%s", hexbuf);
                sprintf(env->me_txns->mti_wmname, "Global\\MDBw%s", hexbuf);
                env->me_rmutex = CreateMutex(&mdb_all_sa, FALSE, env->me_txns->mti_rmname);
                if (!env->me_rmutex) goto fail_errno;
                env->me_wmutex = CreateMutex(&mdb_all_sa, FALSE, env->me_txns->mti_wmname);
                if (!env->me_wmutex) goto fail_errno;
#elif defined(MDB_USE_POSIX_SEM)
                struct stat stbuf;
                struct {
                        dev_t dev;
                        ino_t ino;
                } idbuf;
                MDB_val val;
                char hexbuf[17];

                if (fstat(env->me_lfd, &stbuf)) goto fail_errno;
                idbuf.dev = stbuf.st_dev;
                idbuf.ino = stbuf.st_ino;
                val.mv_data = &idbuf;
                val.mv_size = sizeof(idbuf);
                mdb_hash_hex(&val, hexbuf);
                sprintf(env->me_txns->mti_rmname, "/MDBr%s", hexbuf);
                sprintf(env->me_txns->mti_wmname, "/MDBw%s", hexbuf);
                /* Clean up after a previous run, if needed:  Try to
                 * remove both semaphores before doing anything else.
                 */
                sem_unlink(env->me_txns->mti_rmname);
                sem_unlink(env->me_txns->mti_wmname);
                env->me_rmutex = sem_open(env->me_txns->mti_rmname,
                        O_CREAT|O_EXCL, mode, 1);
                if (env->me_rmutex == SEM_FAILED) goto fail_errno;
                env->me_wmutex = sem_open(env->me_txns->mti_wmname,
                        O_CREAT|O_EXCL, mode, 1);
                if (env->me_wmutex == SEM_FAILED) goto fail_errno;
#else   /* MDB_USE_POSIX_SEM */
                pthread_mutexattr_t mattr;

                if ((rc = pthread_mutexattr_init(&mattr))
                        || (rc = pthread_mutexattr_setpshared(&mattr, PTHREAD_PROCESS_SHARED))
                        || (rc = pthread_mutex_init(&env->me_txns->mti_mutex, &mattr))
                        || (rc = pthread_mutex_init(&env->me_txns->mti_wmutex, &mattr)))
                        goto fail;
                pthread_mutexattr_destroy(&mattr);
#endif  /* _WIN32 || MDB_USE_POSIX_SEM */

                env->me_txns->mti_version = MDB_VERSION;
                env->me_txns->mti_magic = MDB_MAGIC;
                env->me_txns->mti_txnid = 0;
                env->me_txns->mti_numreaders = 0;

        } else {
                if (env->me_txns->mti_magic != MDB_MAGIC) {
                        DPUTS("lock region has invalid magic");
                        rc = MDB_INVALID;
                        goto fail;
                }
                if (env->me_txns->mti_version != MDB_VERSION) {
                        DPRINTF("lock region is version %u, expected version %u",
                                env->me_txns->mti_version, MDB_VERSION);
                        rc = MDB_VERSION_MISMATCH;
                        goto fail;
                }
                rc = ErrCode();
                if (rc && rc != EACCES && rc != EAGAIN) {
                        goto fail;
                }
#ifdef _WIN32
                env->me_rmutex = OpenMutex(SYNCHRONIZE, FALSE, env->me_txns->mti_rmname);
                if (!env->me_rmutex) goto fail_errno;
                env->me_wmutex = OpenMutex(SYNCHRONIZE, FALSE, env->me_txns->mti_wmname);
                if (!env->me_wmutex) goto fail_errno;
#elif defined(MDB_USE_POSIX_SEM)
                env->me_rmutex = sem_open(env->me_txns->mti_rmname, 0);
                if (env->me_rmutex == SEM_FAILED) goto fail_errno;
                env->me_wmutex = sem_open(env->me_txns->mti_wmname, 0);
                if (env->me_wmutex == SEM_FAILED) goto fail_errno;
#endif
        }
        return MDB_SUCCESS;

fail_errno:
        rc = ErrCode();
fail:
        return rc;
}

        /** The name of the lock file in the DB environment */
#define LOCKNAME        "/lock.mdb"
        /** The name of the data file in the DB environment */
#define DATANAME        "/data.mdb"
        /** The suffix of the lock file when no subdir is used */
#define LOCKSUFF        "-lock"
        /** Only a subset of the @ref mdb_env flags can be changed
         *      at runtime. Changing other flags requires closing the
         *      environment and re-opening it with the new flags.
         */
#define CHANGEABLE      (MDB_NOSYNC|MDB_NOMETASYNC|MDB_MAPASYNC)
#define CHANGELESS      (MDB_FIXEDMAP|MDB_NOSUBDIR|MDB_RDONLY|MDB_WRITEMAP|MDB_NOTLS)

int
mdb_env_open(MDB_env *env, const char *path, unsigned int flags, mdb_mode_t mode)
{
        int             oflags, rc, len, excl = -1;
        char *lpath, *dpath;

        if (env->me_fd!=INVALID_HANDLE_VALUE || (flags & ~(CHANGEABLE|CHANGELESS)))
                return EINVAL;

        len = strlen(path);
        if (flags & MDB_NOSUBDIR) {
                rc = len + sizeof(LOCKSUFF) + len + 1;
        } else {
                rc = len + sizeof(LOCKNAME) + len + sizeof(DATANAME);
        }
        lpath = malloc(rc);
        if (!lpath)
                return ENOMEM;
        if (flags & MDB_NOSUBDIR) {
                dpath = lpath + len + sizeof(LOCKSUFF);
                sprintf(lpath, "%s" LOCKSUFF, path);
                strcpy(dpath, path);
        } else {
                dpath = lpath + len + sizeof(LOCKNAME);
                sprintf(lpath, "%s" LOCKNAME, path);
                sprintf(dpath, "%s" DATANAME, path);
        }

        rc = MDB_SUCCESS;
        flags |= env->me_flags;
        if (flags & MDB_RDONLY) {
                /* silently ignore WRITEMAP when we're only getting read access */
                flags &= ~MDB_WRITEMAP;
        } else {
                if (!((env->me_free_pgs = mdb_midl_alloc(MDB_IDL_UM_MAX)) &&
                          (env->me_dirty_list = calloc(MDB_IDL_UM_SIZE, sizeof(MDB_ID2)))))
                        rc = ENOMEM;
        }
        env->me_flags = flags |= MDB_ENV_ACTIVE;
        if (rc)
                goto leave;

        env->me_path = strdup(path);
        env->me_dbxs = calloc(env->me_maxdbs, sizeof(MDB_dbx));
        env->me_dbflags = calloc(env->me_maxdbs, sizeof(uint16_t));
        if (!(env->me_dbxs && env->me_path && env->me_dbflags)) {
                rc = ENOMEM;
                goto leave;
        }

        rc = mdb_env_setup_locks(env, lpath, mode, &excl);
        if (rc)
                goto leave;

#ifdef _WIN32
        if (F_ISSET(flags, MDB_RDONLY)) {
                oflags = GENERIC_READ;
                len = OPEN_EXISTING;
        } else {
                oflags = GENERIC_READ|GENERIC_WRITE;
                len = OPEN_ALWAYS;
        }
        mode = FILE_ATTRIBUTE_NORMAL;
        env->me_fd = CreateFile(dpath, oflags, FILE_SHARE_READ|FILE_SHARE_WRITE,
                NULL, len, mode, NULL);
#else
        if (F_ISSET(flags, MDB_RDONLY))
                oflags = O_RDONLY;
        else
                oflags = O_RDWR | O_CREAT;

        env->me_fd = open(dpath, oflags, mode);
#endif
        if (env->me_fd == INVALID_HANDLE_VALUE) {
                rc = ErrCode();
                goto leave;
        }

        if ((rc = mdb_env_open2(env)) == MDB_SUCCESS) {
                if (flags & (MDB_RDONLY|MDB_WRITEMAP)) {
                        env->me_mfd = env->me_fd;
                } else {
                        /* Synchronous fd for meta writes. Needed even with
                         * MDB_NOSYNC/MDB_NOMETASYNC, in case these get reset.
                         */
#ifdef _WIN32
                        env->me_mfd = CreateFile(dpath, oflags,
                                FILE_SHARE_READ|FILE_SHARE_WRITE, NULL, len,
                                mode | FILE_FLAG_WRITE_THROUGH, NULL);
#else
                        env->me_mfd = open(dpath, oflags | MDB_DSYNC, mode);
#endif
                        if (env->me_mfd == INVALID_HANDLE_VALUE) {
                                rc = ErrCode();
                                goto leave;
                        }
                }
                DPRINTF("opened dbenv %p", (void *) env);
                if (excl > 0) {
                        rc = mdb_env_share_locks(env, &excl);
                }
        }

leave:
        if (rc) {
                mdb_env_close0(env, excl);
        }
        free(lpath);
        return rc;
}

/** Destroy resources from mdb_env_open(), clear our readers & DBIs */
static void
mdb_env_close0(MDB_env *env, int excl)
{
        int i;

        if (!(env->me_flags & MDB_ENV_ACTIVE))
                return;

        /* Doing this here since me_dbxs may not exist during mdb_env_close */
        for (i = env->me_maxdbs; --i > MAIN_DBI; )
                free(env->me_dbxs[i].md_name.mv_data);

        free(env->me_dbflags);
        free(env->me_dbxs);
        free(env->me_path);
        free(env->me_dirty_list);
        mdb_midl_free(env->me_free_pgs);

        if (env->me_flags & MDB_ENV_TXKEY) {
                pthread_key_delete(env->me_txkey);
#ifdef _WIN32
                /* Delete our key from the global list */
                for (i=0; i<mdb_tls_nkeys; i++)
                        if (mdb_tls_keys[i] == env->me_txkey) {
                                mdb_tls_keys[i] = mdb_tls_keys[mdb_tls_nkeys-1];
                                mdb_tls_nkeys--;
                                break;
                        }
#endif
        }

        if (env->me_map) {
                munmap(env->me_map, env->me_mapsize);
        }
        if (env->me_mfd != env->me_fd && env->me_mfd != INVALID_HANDLE_VALUE)
                (void) close(env->me_mfd);
        if (env->me_fd != INVALID_HANDLE_VALUE)
                (void) close(env->me_fd);
        if (env->me_txns) {
                pid_t pid = env->me_pid;
                /* Clearing readers is done in this function because
                 * me_txkey with its destructor must be disabled first.
                 */
                for (i = env->me_numreaders; --i >= 0; )
                        if (env->me_txns->mti_readers[i].mr_pid == pid)
                                env->me_txns->mti_readers[i].mr_pid = 0;
#ifdef _WIN32
                if (env->me_rmutex) {
                        CloseHandle(env->me_rmutex);
                        if (env->me_wmutex) CloseHandle(env->me_wmutex);
                }
                /* Windows automatically destroys the mutexes when
                 * the last handle closes.
                 */
#elif defined(MDB_USE_POSIX_SEM)
                if (env->me_rmutex != SEM_FAILED) {
                        sem_close(env->me_rmutex);
                        if (env->me_wmutex != SEM_FAILED)
                                sem_close(env->me_wmutex);
                        /* If we have the filelock:  If we are the
                         * only remaining user, clean up semaphores.
                         */
                        if (excl == 0)
                                mdb_env_excl_lock(env, &excl);
                        if (excl > 0) {
                                sem_unlink(env->me_txns->mti_rmname);
                                sem_unlink(env->me_txns->mti_wmname);
                        }
                }
#endif
                munmap((void *)env->me_txns, (env->me_maxreaders-1)*sizeof(MDB_reader)+sizeof(MDB_txninfo));
        }
        if (env->me_lfd != INVALID_HANDLE_VALUE) {
#ifdef _WIN32
                if (excl >= 0) {
                        /* Unlock the lockfile.  Windows would have unlocked it
                         * after closing anyway, but not necessarily at once.
                         */
                        UnlockFile(env->me_lfd, 0, 0, 1, 0);
                }
#endif
                (void) close(env->me_lfd);
        }

        env->me_flags &= ~(MDB_ENV_ACTIVE|MDB_ENV_TXKEY);
}

int
mdb_env_copyfd(MDB_env *env, HANDLE fd)
{
        MDB_txn *txn = NULL;
        int rc;
        size_t wsize;
        char *ptr;

        /* Do the lock/unlock of the reader mutex before starting the
         * write txn.  Otherwise other read txns could block writers.
         */
        rc = mdb_txn_begin(env, NULL, MDB_RDONLY, &txn);
        if (rc)
                return rc;

        if (env->me_txns) {
                /* We must start the actual read txn after blocking writers */
                mdb_txn_reset0(txn, "reset-stage1");

                /* Temporarily block writers until we snapshot the meta pages */
                LOCK_MUTEX_W(env);

                rc = mdb_txn_renew0(txn);
                if (rc) {
                        UNLOCK_MUTEX_W(env);
                        goto leave;
                }
        }

        wsize = env->me_psize * 2;
#ifdef _WIN32
        {
                DWORD len;
                rc = WriteFile(fd, env->me_map, wsize, &len, NULL);
                rc = rc ? (len == wsize ? MDB_SUCCESS : EIO) : ErrCode();
        }
#else
        rc = write(fd, env->me_map, wsize);
        rc = rc == (int)wsize ? MDB_SUCCESS : rc < 0 ? ErrCode() : EIO;
#endif
        if (env->me_txns)
                UNLOCK_MUTEX_W(env);

        if (rc)
                goto leave;

        ptr = env->me_map + wsize;
        wsize = txn->mt_next_pgno * env->me_psize - wsize;
#ifdef _WIN32
        while (wsize > 0) {
                DWORD len, w2;
                if (wsize > MAX_WRITE)
                        w2 = MAX_WRITE;
                else
                        w2 = wsize;
                rc = WriteFile(fd, ptr, w2, &len, NULL);
                rc = rc ? (len == w2 ? MDB_SUCCESS : EIO) : ErrCode();
                if (rc) break;
                wsize -= w2;
                ptr += w2;
        }
#else
        while (wsize > 0) {
                size_t w2;
                ssize_t wres;
                if (wsize > MAX_WRITE)
                        w2 = MAX_WRITE;
                else
                        w2 = wsize;
                wres = write(fd, ptr, w2);
                rc = wres == (ssize_t)w2 ? MDB_SUCCESS : wres < 0 ? ErrCode() : EIO;
                if (rc) break;
                wsize -= wres;
                ptr += wres;
        }
#endif

leave:
        mdb_txn_abort(txn);
        return rc;
}

int
mdb_env_copy(MDB_env *env, const char *path)
{
        int rc, len;
        char *lpath;
        HANDLE newfd = INVALID_HANDLE_VALUE;

        if (env->me_flags & MDB_NOSUBDIR) {
                lpath = (char *)path;
        } else {
                len = strlen(path);
                len += sizeof(DATANAME);
                lpath = malloc(len);
                if (!lpath)
                        return ENOMEM;
                sprintf(lpath, "%s" DATANAME, path);
        }

        /* The destination path must exist, but the destination file must not.
         * We don't want the OS to cache the writes, since the source data is
         * already in the OS cache.
         */
#ifdef _WIN32
        newfd = CreateFile(lpath, GENERIC_WRITE, 0, NULL, CREATE_NEW,
                                FILE_FLAG_NO_BUFFERING|FILE_FLAG_WRITE_THROUGH, NULL);
#else
        newfd = open(lpath, O_WRONLY|O_CREAT|O_EXCL
#ifdef O_DIRECT
                |O_DIRECT
#endif
                , 0666);
#endif
        if (newfd == INVALID_HANDLE_VALUE) {
                rc = ErrCode();
                goto leave;
        }

#ifdef F_NOCACHE        /* __APPLE__ */
        rc = fcntl(newfd, F_NOCACHE, 1);
        if (rc) {
                rc = ErrCode();
                goto leave;
        }
#endif

        rc = mdb_env_copyfd(env, newfd);

leave:
        if (!(env->me_flags & MDB_NOSUBDIR))
                free(lpath);
        if (newfd != INVALID_HANDLE_VALUE)
                if (close(newfd) < 0 && rc == MDB_SUCCESS)
                        rc = ErrCode();

        return rc;
}

void
mdb_env_close(MDB_env *env)
{
        MDB_page *dp;

        if (env == NULL)
                return;

        VGMEMP_DESTROY(env);
        while ((dp = env->me_dpages) != NULL) {
                VGMEMP_DEFINED(&dp->mp_next, sizeof(dp->mp_next));
                env->me_dpages = dp->mp_next;
                free(dp);
        }

        mdb_env_close0(env, 0);
        free(env);
}

/** Compare two items pointing at aligned size_t's */
static int
mdb_cmp_long(const MDB_val *a, const MDB_val *b)
{
        return (*(size_t *)a->mv_data < *(size_t *)b->mv_data) ? -1 :
                *(size_t *)a->mv_data > *(size_t *)b->mv_data;
}

/** Compare two items pointing at aligned int's */
static int
mdb_cmp_int(const MDB_val *a, const MDB_val *b)
{
        return (*(unsigned int *)a->mv_data < *(unsigned int *)b->mv_data) ? -1 :
                *(unsigned int *)a->mv_data > *(unsigned int *)b->mv_data;
}

/** Compare two items pointing at ints of unknown alignment.
 *      Nodes and keys are guaranteed to be 2-byte aligned.
 */
static int
mdb_cmp_cint(const MDB_val *a, const MDB_val *b)
{
#if BYTE_ORDER == LITTLE_ENDIAN
        unsigned short *u, *c;
        int x;

        u = (unsigned short *) ((char *) a->mv_data + a->mv_size);
        c = (unsigned short *) ((char *) b->mv_data + a->mv_size);
        do {
                x = *--u - *--c;
        } while(!x && u > (unsigned short *)a->mv_data);
        return x;
#else
        return memcmp(a->mv_data, b->mv_data, a->mv_size);
#endif
}

/** Compare two items lexically */
static int
mdb_cmp_memn(const MDB_val *a, const MDB_val *b)
{
        int diff;
        ssize_t len_diff;
        unsigned int len;

        len = a->mv_size;
        len_diff = (ssize_t) a->mv_size - (ssize_t) b->mv_size;
        if (len_diff > 0) {
                len = b->mv_size;
                len_diff = 1;
        }

        diff = memcmp(a->mv_data, b->mv_data, len);
        return diff ? diff : len_diff<0 ? -1 : len_diff;
}

/** Compare two items in reverse byte order */
static int
mdb_cmp_memnr(const MDB_val *a, const MDB_val *b)
{
        const unsigned char     *p1, *p2, *p1_lim;
        ssize_t len_diff;
        int diff;

        p1_lim = (const unsigned char *)a->mv_data;
        p1 = (const unsigned char *)a->mv_data + a->mv_size;
        p2 = (const unsigned char *)b->mv_data + b->mv_size;

        len_diff = (ssize_t) a->mv_size - (ssize_t) b->mv_size;
        if (len_diff > 0) {
                p1_lim += len_diff;
                len_diff = 1;
        }

        while (p1 > p1_lim) {
                diff = *--p1 - *--p2;
                if (diff)
                        return diff;
        }
        return len_diff<0 ? -1 : len_diff;
}

/** Search for key within a page, using binary search.
 * Returns the smallest entry larger or equal to the key.
 * If exactp is non-null, stores whether the found entry was an exact match
 * in *exactp (1 or 0).
 * Updates the cursor index with the index of the found entry.
 * If no entry larger or equal to the key is found, returns NULL.
 */
static MDB_node *
mdb_node_search(MDB_cursor *mc, MDB_val *key, int *exactp)
{
        unsigned int     i = 0, nkeys;
        int              low, high;
        int              rc = 0;
        MDB_page *mp = mc->mc_pg[mc->mc_top];
        MDB_node        *node = NULL;
        MDB_val  nodekey;
        MDB_cmp_func *cmp;
        DKBUF;

        nkeys = NUMKEYS(mp);

#if MDB_DEBUG
        {
        pgno_t pgno;
        COPY_PGNO(pgno, mp->mp_pgno);
        DPRINTF("searching %u keys in %s %spage %zu",
            nkeys, IS_LEAF(mp) ? "leaf" : "branch", IS_SUBP(mp) ? "sub-" : "",
            pgno);
        }
#endif

        assert(nkeys > 0);

        low = IS_LEAF(mp) ? 0 : 1;
        high = nkeys - 1;
        cmp = mc->mc_dbx->md_cmp;

        /* Branch pages have no data, so if using integer keys,
         * alignment is guaranteed. Use faster mdb_cmp_int.
         */
        if (cmp == mdb_cmp_cint && IS_BRANCH(mp)) {
                if (NODEPTR(mp, 1)->mn_ksize == sizeof(size_t))
                        cmp = mdb_cmp_long;
                else
                        cmp = mdb_cmp_int;
        }

        if (IS_LEAF2(mp)) {
                nodekey.mv_size = mc->mc_db->md_pad;
                node = NODEPTR(mp, 0);  /* fake */
                while (low <= high) {
                        i = (low + high) >> 1;
                        nodekey.mv_data = LEAF2KEY(mp, i, nodekey.mv_size);
                        rc = cmp(key, &nodekey);
                        DPRINTF("found leaf index %u [%s], rc = %i",
                            i, DKEY(&nodekey), rc);
                        if (rc == 0)
                                break;
                        if (rc > 0)
                                low = i + 1;
                        else
                                high = i - 1;
                }
        } else {
                while (low <= high) {
                        i = (low + high) >> 1;

                        node = NODEPTR(mp, i);
                        nodekey.mv_size = NODEKSZ(node);
                        nodekey.mv_data = NODEKEY(node);

                        rc = cmp(key, &nodekey);
#if MDB_DEBUG
                        if (IS_LEAF(mp))
                                DPRINTF("found leaf index %u [%s], rc = %i",
                                    i, DKEY(&nodekey), rc);
                        else
                                DPRINTF("found branch index %u [%s -> %zu], rc = %i",
                                    i, DKEY(&nodekey), NODEPGNO(node), rc);
#endif
                        if (rc == 0)
                                break;
                        if (rc > 0)
                                low = i + 1;
                        else
                                high = i - 1;
                }
        }

        if (rc > 0) {   /* Found entry is less than the key. */
                i++;    /* Skip to get the smallest entry larger than key. */
                if (!IS_LEAF2(mp))
                        node = NODEPTR(mp, i);
        }
        if (exactp)
                *exactp = (rc == 0);
        /* store the key index */
        mc->mc_ki[mc->mc_top] = i;
        if (i >= nkeys)
                /* There is no entry larger or equal to the key. */
                return NULL;

        /* nodeptr is fake for LEAF2 */
        return node;
}

#if 0
static void
mdb_cursor_adjust(MDB_cursor *mc, func)
{
        MDB_cursor *m2;

        for (m2 = mc->mc_txn->mt_cursors[mc->mc_dbi]; m2; m2=m2->mc_next) {
                if (m2->mc_pg[m2->mc_top] == mc->mc_pg[mc->mc_top]) {
                        func(mc, m2);
                }
        }
}
#endif

/** Pop a page off the top of the cursor's stack. */
static void
mdb_cursor_pop(MDB_cursor *mc)
{
        if (mc->mc_snum) {
#ifndef MDB_DEBUG_SKIP
                MDB_page        *top = mc->mc_pg[mc->mc_top];
#endif
                mc->mc_snum--;
                if (mc->mc_snum)
                        mc->mc_top--;

                DPRINTF("popped page %zu off db %u cursor %p", top->mp_pgno,
                        mc->mc_dbi, (void *) mc);
        }
}

/** Push a page onto the top of the cursor's stack. */
static int
mdb_cursor_push(MDB_cursor *mc, MDB_page *mp)
{
        DPRINTF("pushing page %zu on db %u cursor %p", mp->mp_pgno,
                mc->mc_dbi, (void *) mc);

        if (mc->mc_snum >= CURSOR_STACK) {
                assert(mc->mc_snum < CURSOR_STACK);
                return MDB_CURSOR_FULL;
        }

        mc->mc_top = mc->mc_snum++;
        mc->mc_pg[mc->mc_top] = mp;
        mc->mc_ki[mc->mc_top] = 0;

        return MDB_SUCCESS;
}

/** Find the address of the page corresponding to a given page number.
 * @param[in] txn the transaction for this access.
 * @param[in] pgno the page number for the page to retrieve.
 * @param[out] ret address of a pointer where the page's address will be stored.
 * @param[out] lvl dirty_list inheritance level of found page. 1=current txn, 0=mapped page.
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_page_get(MDB_txn *txn, pgno_t pgno, MDB_page **ret, int *lvl)
{
        MDB_page *p = NULL;
        int level;

        if (!((txn->mt_flags & MDB_TXN_RDONLY) |
                  (txn->mt_env->me_flags & MDB_WRITEMAP)))
        {
                MDB_txn *tx2 = txn;
                level = 1;
                do {
                        MDB_ID2L dl = tx2->mt_u.dirty_list;
                        unsigned x;
                        /* Spilled pages were dirtied in this txn and flushed
                         * because the dirty list got full. Bring this page
                         * back in from the map (but don't unspill it here,
                         * leave that unless page_touch happens again).
                         */
                        if (tx2->mt_spill_pgs) {
                                x = mdb_midl_search(tx2->mt_spill_pgs, pgno);
                                if (x <= tx2->mt_spill_pgs[0] && tx2->mt_spill_pgs[x] == pgno) {
                                        p = (MDB_page *)(txn->mt_env->me_map + txn->mt_env->me_psize * pgno);
                                        goto done;
                                }
                        }
                        if (dl[0].mid) {
                                unsigned x = mdb_mid2l_search(dl, pgno);
                                if (x <= dl[0].mid && dl[x].mid == pgno) {
                                        p = dl[x].mptr;
                                        goto done;
                                }
                        }
                        level++;
                } while ((tx2 = tx2->mt_parent) != NULL);
        }

        if (pgno < txn->mt_next_pgno) {
                level = 0;
                p = (MDB_page *)(txn->mt_env->me_map + txn->mt_env->me_psize * pgno);
        } else {
                DPRINTF("page %zu not found", pgno);
                assert(p != NULL);
                return MDB_PAGE_NOTFOUND;
        }

done:
        *ret = p;
        if (lvl)
                *lvl = level;
        return MDB_SUCCESS;
}

/** Search for the page a given key should be in.
 * Pushes parent pages on the cursor stack. This function continues a
 * search on a cursor that has already been initialized. (Usually by
 * #mdb_page_search() but also by #mdb_node_move().)
 * @param[in,out] mc the cursor for this operation.
 * @param[in] key the key to search for. If NULL, search for the lowest
 * page. (This is used by #mdb_cursor_first().)
 * @param[in] modify If true, visited pages are updated with new page numbers.
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_page_search_root(MDB_cursor *mc, MDB_val *key, int modify)
{
        MDB_page        *mp = mc->mc_pg[mc->mc_top];
        DKBUF;
        int rc;


        while (IS_BRANCH(mp)) {
                MDB_node        *node;
                indx_t          i;

                DPRINTF("branch page %zu has %u keys", mp->mp_pgno, NUMKEYS(mp));
                assert(NUMKEYS(mp) > 1);
                DPRINTF("found index 0 to page %zu", NODEPGNO(NODEPTR(mp, 0)));

                if (key == NULL)        /* Initialize cursor to first page. */
                        i = 0;
                else if (key->mv_size > MDB_MAXKEYSIZE && key->mv_data == NULL) {
                                                        /* cursor to last page */
                        i = NUMKEYS(mp)-1;
                } else {
                        int      exact;
                        node = mdb_node_search(mc, key, &exact);
                        if (node == NULL)
                                i = NUMKEYS(mp) - 1;
                        else {
                                i = mc->mc_ki[mc->mc_top];
                                if (!exact) {
                                        assert(i > 0);
                                        i--;
                                }
                        }
                }

                if (key)
                        DPRINTF("following index %u for key [%s]",
                            i, DKEY(key));
                assert(i < NUMKEYS(mp));
                node = NODEPTR(mp, i);

                if ((rc = mdb_page_get(mc->mc_txn, NODEPGNO(node), &mp, NULL)) != 0)
                        return rc;

                mc->mc_ki[mc->mc_top] = i;
                if ((rc = mdb_cursor_push(mc, mp)))
                        return rc;

                if (modify) {
                        if ((rc = mdb_page_touch(mc)) != 0)
                                return rc;
                        mp = mc->mc_pg[mc->mc_top];
                }
        }

        if (!IS_LEAF(mp)) {
                DPRINTF("internal error, index points to a %02X page!?",
                    mp->mp_flags);
                return MDB_CORRUPTED;
        }

        DPRINTF("found leaf page %zu for key [%s]", mp->mp_pgno,
            key ? DKEY(key) : NULL);
        mc->mc_flags |= C_INITIALIZED;
        mc->mc_flags &= ~C_EOF;

        return MDB_SUCCESS;
}

/** Search for the lowest key under the current branch page.
 * This just bypasses a NUMKEYS check in the current page
 * before calling mdb_page_search_root(), because the callers
 * are all in situations where the current page is known to
 * be underfilled.
 */
static int
mdb_page_search_lowest(MDB_cursor *mc)
{
        MDB_page        *mp = mc->mc_pg[mc->mc_top];
        MDB_node        *node = NODEPTR(mp, 0);
        int rc;

        if ((rc = mdb_page_get(mc->mc_txn, NODEPGNO(node), &mp, NULL)) != 0)
                return rc;

        mc->mc_ki[mc->mc_top] = 0;
        if ((rc = mdb_cursor_push(mc, mp)))
                return rc;
        return mdb_page_search_root(mc, NULL, 0);
}

/** Search for the page a given key should be in.
 * Pushes parent pages on the cursor stack. This function just sets up
 * the search; it finds the root page for \b mc's database and sets this
 * as the root of the cursor's stack. Then #mdb_page_search_root() is
 * called to complete the search.
 * @param[in,out] mc the cursor for this operation.
 * @param[in] key the key to search for. If NULL, search for the lowest
 * page. (This is used by #mdb_cursor_first().)
 * @param[in] flags If MDB_PS_MODIFY set, visited pages are updated with new page numbers.
 *   If MDB_PS_ROOTONLY set, just fetch root node, no further lookups.
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_page_search(MDB_cursor *mc, MDB_val *key, int flags)
{
        int              rc;
        pgno_t           root;

        /* Make sure the txn is still viable, then find the root from
         * the txn's db table.
         */
        if (F_ISSET(mc->mc_txn->mt_flags, MDB_TXN_ERROR)) {
                DPUTS("transaction has failed, must abort");
                return EINVAL;
        } else {
                /* Make sure we're using an up-to-date root */
                if (mc->mc_dbi > MAIN_DBI) {
                        if ((*mc->mc_dbflag & DB_STALE) ||
                        ((flags & MDB_PS_MODIFY) && !(*mc->mc_dbflag & DB_DIRTY))) {
                                MDB_cursor mc2;
                                unsigned char dbflag = 0;
                                mdb_cursor_init(&mc2, mc->mc_txn, MAIN_DBI, NULL);
                                rc = mdb_page_search(&mc2, &mc->mc_dbx->md_name, flags & MDB_PS_MODIFY);
                                if (rc)
                                        return rc;
                                if (*mc->mc_dbflag & DB_STALE) {
                                        MDB_val data;
                                        int exact = 0;
                                        uint16_t flags;
                                        MDB_node *leaf = mdb_node_search(&mc2,
                                                &mc->mc_dbx->md_name, &exact);
                                        if (!exact)
                                                return MDB_NOTFOUND;
                                        rc = mdb_node_read(mc->mc_txn, leaf, &data);
                                        if (rc)
                                                return rc;
                                        memcpy(&flags, ((char *) data.mv_data + offsetof(MDB_db, md_flags)),
                                                sizeof(uint16_t));
                                        /* The txn may not know this DBI, or another process may
                                         * have dropped and recreated the DB with other flags.
                                         */
                                        if ((mc->mc_db->md_flags & PERSISTENT_FLAGS) != flags)
                                                return MDB_INCOMPATIBLE;
                                        memcpy(mc->mc_db, data.mv_data, sizeof(MDB_db));
                                }
                                if (flags & MDB_PS_MODIFY)
                                        dbflag = DB_DIRTY;
                                *mc->mc_dbflag &= ~DB_STALE;
                                *mc->mc_dbflag |= dbflag;
                        }
                }
                root = mc->mc_db->md_root;

                if (root == P_INVALID) {                /* Tree is empty. */
                        DPUTS("tree is empty");
                        return MDB_NOTFOUND;
                }
        }

        assert(root > 1);
        if (!mc->mc_pg[0] || mc->mc_pg[0]->mp_pgno != root)
                if ((rc = mdb_page_get(mc->mc_txn, root, &mc->mc_pg[0], NULL)) != 0)
                        return rc;

        mc->mc_snum = 1;
        mc->mc_top = 0;

        DPRINTF("db %u root page %zu has flags 0x%X",
                mc->mc_dbi, root, mc->mc_pg[0]->mp_flags);

        if (flags & MDB_PS_MODIFY) {
                if ((rc = mdb_page_touch(mc)))
                        return rc;
        }

        if (flags & MDB_PS_ROOTONLY)
                return MDB_SUCCESS;

        return mdb_page_search_root(mc, key, flags);
}

static int
mdb_ovpage_free(MDB_cursor *mc, MDB_page *mp)
{
        MDB_txn *txn = mc->mc_txn;
        pgno_t pg = mp->mp_pgno;
        unsigned i, ovpages = mp->mp_pages;
        MDB_env *env = txn->mt_env;
        int rc;

        DPRINTF("free ov page %zu (%d)", pg, ovpages);
        /* If the page is dirty or on the spill list we just acquired it,
         * so we should give it back to our current free list, if any.
         * Not currently supported in nested txns.
         * Otherwise put it onto the list of pages we freed in this txn.
         */
        if (!(mp->mp_flags & P_DIRTY) && txn->mt_spill_pgs) {
                unsigned x = mdb_midl_search(txn->mt_spill_pgs, pg);
                if (x <= txn->mt_spill_pgs[0] && txn->mt_spill_pgs[x] == pg) {
                        /* This page is no longer spilled */
                        for (; x < txn->mt_spill_pgs[0]; x++)
                                txn->mt_spill_pgs[x] = txn->mt_spill_pgs[x+1];
                        txn->mt_spill_pgs[0]--;
                        goto release;
                }
        }
        if ((mp->mp_flags & P_DIRTY) && !txn->mt_parent && env->me_pghead) {
                unsigned j, x;
                pgno_t *mop;
                MDB_ID2 *dl, ix, iy;
                rc = mdb_midl_need(&env->me_pghead, ovpages);
                if (rc)
                        return rc;
                /* Remove from dirty list */
                dl = txn->mt_u.dirty_list;
                x = dl[0].mid--;
                for (ix = dl[x]; ix.mptr != mp; ix = iy) {
                        if (x > 1) {
                                x--;
                                iy = dl[x];
                                dl[x] = ix;
                        } else {
                                assert(x > 1);
                                j = ++(dl[0].mid);
                                dl[j] = ix;             /* Unsorted. OK when MDB_TXN_ERROR. */
                                txn->mt_flags |= MDB_TXN_ERROR;
                                return MDB_CORRUPTED;
                        }
                }
                if (!(env->me_flags & MDB_WRITEMAP))
                        mdb_dpage_free(env, mp);
release:
                /* Insert in me_pghead */
                mop = env->me_pghead;
                j = mop[0] + ovpages;
                for (i = mop[0]; i && mop[i] < pg; i--)
                        mop[j--] = mop[i];
                while (j>i)
                        mop[j--] = pg++;
                mop[0] += ovpages;
        } else {
                rc = mdb_midl_append_range(&txn->mt_free_pgs, pg, ovpages);
                if (rc)
                        return rc;
        }
        mc->mc_db->md_overflow_pages -= ovpages;
        return 0;
}

/** Return the data associated with a given node.
 * @param[in] txn The transaction for this operation.
 * @param[in] leaf The node being read.
 * @param[out] data Updated to point to the node's data.
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_node_read(MDB_txn *txn, MDB_node *leaf, MDB_val *data)
{
        MDB_page        *omp;           /* overflow page */
        pgno_t           pgno;
        int rc;

        if (!F_ISSET(leaf->mn_flags, F_BIGDATA)) {
                data->mv_size = NODEDSZ(leaf);
                data->mv_data = NODEDATA(leaf);
                return MDB_SUCCESS;
        }

        /* Read overflow data.
         */
        data->mv_size = NODEDSZ(leaf);
        memcpy(&pgno, NODEDATA(leaf), sizeof(pgno));
        if ((rc = mdb_page_get(txn, pgno, &omp, NULL)) != 0) {
                DPRINTF("read overflow page %zu failed", pgno);
                return rc;
        }
        data->mv_data = METADATA(omp);

        return MDB_SUCCESS;
}

int
mdb_get(MDB_txn *txn, MDB_dbi dbi,
    MDB_val *key, MDB_val *data)
{
        MDB_cursor      mc;
        MDB_xcursor     mx;
        int exact = 0;
        DKBUF;

        assert(key);
        assert(data);
        DPRINTF("===> get db %u key [%s]", dbi, DKEY(key));

        if (txn == NULL || !dbi || dbi >= txn->mt_numdbs || !(txn->mt_dbflags[dbi] & DB_VALID))
                return EINVAL;

        if (key->mv_size == 0 || key->mv_size > MDB_MAXKEYSIZE) {
                return EINVAL;
        }

        mdb_cursor_init(&mc, txn, dbi, &mx);
        return mdb_cursor_set(&mc, key, data, MDB_SET, &exact);
}

/** Find a sibling for a page.
 * Replaces the page at the top of the cursor's stack with the
 * specified sibling, if one exists.
 * @param[in] mc The cursor for this operation.
 * @param[in] move_right Non-zero if the right sibling is requested,
 * otherwise the left sibling.
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_cursor_sibling(MDB_cursor *mc, int move_right)
{
        int              rc;
        MDB_node        *indx;
        MDB_page        *mp;

        if (mc->mc_snum < 2) {
                return MDB_NOTFOUND;            /* root has no siblings */
        }

        mdb_cursor_pop(mc);
        DPRINTF("parent page is page %zu, index %u",
                mc->mc_pg[mc->mc_top]->mp_pgno, mc->mc_ki[mc->mc_top]);

        if (move_right ? (mc->mc_ki[mc->mc_top] + 1u >= NUMKEYS(mc->mc_pg[mc->mc_top]))
                       : (mc->mc_ki[mc->mc_top] == 0)) {
                DPRINTF("no more keys left, moving to %s sibling",
                    move_right ? "right" : "left");
                if ((rc = mdb_cursor_sibling(mc, move_right)) != MDB_SUCCESS) {
                        /* undo cursor_pop before returning */
                        mc->mc_top++;
                        mc->mc_snum++;
                        return rc;
                }
        } else {
                if (move_right)
                        mc->mc_ki[mc->mc_top]++;
                else
                        mc->mc_ki[mc->mc_top]--;
                DPRINTF("just moving to %s index key %u",
                    move_right ? "right" : "left", mc->mc_ki[mc->mc_top]);
        }
        assert(IS_BRANCH(mc->mc_pg[mc->mc_top]));

        indx = NODEPTR(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);
        if ((rc = mdb_page_get(mc->mc_txn, NODEPGNO(indx), &mp, NULL) != 0))
                return rc;

        mdb_cursor_push(mc, mp);
        if (!move_right)
                mc->mc_ki[mc->mc_top] = NUMKEYS(mp)-1;

        return MDB_SUCCESS;
}

/** Move the cursor to the next data item. */
static int
mdb_cursor_next(MDB_cursor *mc, MDB_val *key, MDB_val *data, MDB_cursor_op op)
{
        MDB_page        *mp;
        MDB_node        *leaf;
        int rc;

        if (mc->mc_flags & C_EOF) {
                return MDB_NOTFOUND;
        }

        assert(mc->mc_flags & C_INITIALIZED);

        mp = mc->mc_pg[mc->mc_top];

        if (mc->mc_db->md_flags & MDB_DUPSORT) {
                leaf = NODEPTR(mp, mc->mc_ki[mc->mc_top]);
                if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
                        if (op == MDB_NEXT || op == MDB_NEXT_DUP) {
                                rc = mdb_cursor_next(&mc->mc_xcursor->mx_cursor, data, NULL, MDB_NEXT);
                                if (op != MDB_NEXT || rc != MDB_NOTFOUND)
                                        return rc;
                        }
                } else {
                        mc->mc_xcursor->mx_cursor.mc_flags &= ~(C_INITIALIZED|C_EOF);
                        if (op == MDB_NEXT_DUP)
                                return MDB_NOTFOUND;
                }
        }

        DPRINTF("cursor_next: top page is %zu in cursor %p", mp->mp_pgno, (void *) mc);

        if (mc->mc_ki[mc->mc_top] + 1u >= NUMKEYS(mp)) {
                DPUTS("=====> move to next sibling page");
                if ((rc = mdb_cursor_sibling(mc, 1)) != MDB_SUCCESS) {
                        mc->mc_flags |= C_EOF;
                        return rc;
                }
                mp = mc->mc_pg[mc->mc_top];
                DPRINTF("next page is %zu, key index %u", mp->mp_pgno, mc->mc_ki[mc->mc_top]);
        } else
                mc->mc_ki[mc->mc_top]++;

        DPRINTF("==> cursor points to page %zu with %u keys, key index %u",
            mp->mp_pgno, NUMKEYS(mp), mc->mc_ki[mc->mc_top]);

        if (IS_LEAF2(mp)) {
                key->mv_size = mc->mc_db->md_pad;
                key->mv_data = LEAF2KEY(mp, mc->mc_ki[mc->mc_top], key->mv_size);
                return MDB_SUCCESS;
        }

        assert(IS_LEAF(mp));
        leaf = NODEPTR(mp, mc->mc_ki[mc->mc_top]);

        if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
                mdb_xcursor_init1(mc, leaf);
        }
        if (data) {
                if ((rc = mdb_node_read(mc->mc_txn, leaf, data)) != MDB_SUCCESS)
                        return rc;

                if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
                        rc = mdb_cursor_first(&mc->mc_xcursor->mx_cursor, data, NULL);
                        if (rc != MDB_SUCCESS)
                                return rc;
                }
        }

        MDB_GET_KEY(leaf, key);
        return MDB_SUCCESS;
}

/** Move the cursor to the previous data item. */
static int
mdb_cursor_prev(MDB_cursor *mc, MDB_val *key, MDB_val *data, MDB_cursor_op op)
{
        MDB_page        *mp;
        MDB_node        *leaf;
        int rc;

        assert(mc->mc_flags & C_INITIALIZED);

        mp = mc->mc_pg[mc->mc_top];

        if (mc->mc_db->md_flags & MDB_DUPSORT) {
                leaf = NODEPTR(mp, mc->mc_ki[mc->mc_top]);
                if (op == MDB_PREV || op == MDB_PREV_DUP) {
                        if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
                                rc = mdb_cursor_prev(&mc->mc_xcursor->mx_cursor, data, NULL, MDB_PREV);
                                if (op != MDB_PREV || rc != MDB_NOTFOUND)
                                        return rc;
                        } else {
                                mc->mc_xcursor->mx_cursor.mc_flags &= ~(C_INITIALIZED|C_EOF);
                                if (op == MDB_PREV_DUP)
                                        return MDB_NOTFOUND;
                        }
                }
        }

        DPRINTF("cursor_prev: top page is %zu in cursor %p", mp->mp_pgno, (void *) mc);

        if (mc->mc_ki[mc->mc_top] == 0)  {
                DPUTS("=====> move to prev sibling page");
                if ((rc = mdb_cursor_sibling(mc, 0)) != MDB_SUCCESS) {
                        return rc;
                }
                mp = mc->mc_pg[mc->mc_top];
                mc->mc_ki[mc->mc_top] = NUMKEYS(mp) - 1;
                DPRINTF("prev page is %zu, key index %u", mp->mp_pgno, mc->mc_ki[mc->mc_top]);
        } else
                mc->mc_ki[mc->mc_top]--;

        mc->mc_flags &= ~C_EOF;

        DPRINTF("==> cursor points to page %zu with %u keys, key index %u",
            mp->mp_pgno, NUMKEYS(mp), mc->mc_ki[mc->mc_top]);

        if (IS_LEAF2(mp)) {
                key->mv_size = mc->mc_db->md_pad;
                key->mv_data = LEAF2KEY(mp, mc->mc_ki[mc->mc_top], key->mv_size);
                return MDB_SUCCESS;
        }

        assert(IS_LEAF(mp));
        leaf = NODEPTR(mp, mc->mc_ki[mc->mc_top]);

        if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
                mdb_xcursor_init1(mc, leaf);
        }
        if (data) {
                if ((rc = mdb_node_read(mc->mc_txn, leaf, data)) != MDB_SUCCESS)
                        return rc;

                if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
                        rc = mdb_cursor_last(&mc->mc_xcursor->mx_cursor, data, NULL);
                        if (rc != MDB_SUCCESS)
                                return rc;
                }
        }

        MDB_GET_KEY(leaf, key);
        return MDB_SUCCESS;
}

/** Set the cursor on a specific data item. */
static int
mdb_cursor_set(MDB_cursor *mc, MDB_val *key, MDB_val *data,
    MDB_cursor_op op, int *exactp)
{
        int              rc;
        MDB_page        *mp;
        MDB_node        *leaf = NULL;
        DKBUF;

        assert(mc);
        assert(key);
        assert(key->mv_size > 0);

        if (mc->mc_db->md_flags & MDB_DUPSORT)
                mc->mc_xcursor->mx_cursor.mc_flags &= ~(C_INITIALIZED|C_EOF);

        /* See if we're already on the right page */
        if (mc->mc_flags & C_INITIALIZED) {
                MDB_val nodekey;

                mp = mc->mc_pg[mc->mc_top];
                if (!NUMKEYS(mp)) {
                        mc->mc_ki[mc->mc_top] = 0;
                        return MDB_NOTFOUND;
                }
                if (mp->mp_flags & P_LEAF2) {
                        nodekey.mv_size = mc->mc_db->md_pad;
                        nodekey.mv_data = LEAF2KEY(mp, 0, nodekey.mv_size);
                } else {
                        leaf = NODEPTR(mp, 0);
                        MDB_GET_KEY(leaf, &nodekey);
                }
                rc = mc->mc_dbx->md_cmp(key, &nodekey);
                if (rc == 0) {
                        /* Probably happens rarely, but first node on the page
                         * was the one we wanted.
                         */
                        mc->mc_ki[mc->mc_top] = 0;
                        if (exactp)
                                *exactp = 1;
                        goto set1;
                }
                if (rc > 0) {
                        unsigned int i;
                        unsigned int nkeys = NUMKEYS(mp);
                        if (nkeys > 1) {
                                if (mp->mp_flags & P_LEAF2) {
                                        nodekey.mv_data = LEAF2KEY(mp,
                                                 nkeys-1, nodekey.mv_size);
                                } else {
                                        leaf = NODEPTR(mp, nkeys-1);
                                        MDB_GET_KEY(leaf, &nodekey);
                                }
                                rc = mc->mc_dbx->md_cmp(key, &nodekey);
                                if (rc == 0) {
                                        /* last node was the one we wanted */
                                        mc->mc_ki[mc->mc_top] = nkeys-1;
                                        if (exactp)
                                                *exactp = 1;
                                        goto set1;
                                }
                                if (rc < 0) {
                                        if (mc->mc_ki[mc->mc_top] < NUMKEYS(mp)) {
                                                /* This is definitely the right page, skip search_page */
                                                if (mp->mp_flags & P_LEAF2) {
                                                        nodekey.mv_data = LEAF2KEY(mp,
                                                                 mc->mc_ki[mc->mc_top], nodekey.mv_size);
                                                } else {
                                                        leaf = NODEPTR(mp, mc->mc_ki[mc->mc_top]);
                                                        MDB_GET_KEY(leaf, &nodekey);
                                                }
                                                rc = mc->mc_dbx->md_cmp(key, &nodekey);
                                                if (rc == 0) {
                                                        /* current node was the one we wanted */
                                                        if (exactp)
                                                                *exactp = 1;
                                                        goto set1;
                                                }
                                        }
                                        rc = 0;
                                        goto set2;
                                }
                        }
                        /* If any parents have right-sibs, search.
                         * Otherwise, there's nothing further.
                         */
                        for (i=0; i<mc->mc_top; i++)
                                if (mc->mc_ki[i] <
                                        NUMKEYS(mc->mc_pg[i])-1)
                                        break;
                        if (i == mc->mc_top) {
                                /* There are no other pages */
                                mc->mc_ki[mc->mc_top] = nkeys;
                                return MDB_NOTFOUND;
                        }
                }
                if (!mc->mc_top) {
                        /* There are no other pages */
                        mc->mc_ki[mc->mc_top] = 0;
                        return MDB_NOTFOUND;
                }
        }

        rc = mdb_page_search(mc, key, 0);
        if (rc != MDB_SUCCESS)
                return rc;

        mp = mc->mc_pg[mc->mc_top];
        assert(IS_LEAF(mp));

set2:
        leaf = mdb_node_search(mc, key, exactp);
        if (exactp != NULL && !*exactp) {
                /* MDB_SET specified and not an exact match. */
                return MDB_NOTFOUND;
        }

        if (leaf == NULL) {
                DPUTS("===> inexact leaf not found, goto sibling");
                if ((rc = mdb_cursor_sibling(mc, 1)) != MDB_SUCCESS)
                        return rc;              /* no entries matched */
                mp = mc->mc_pg[mc->mc_top];
                assert(IS_LEAF(mp));
                leaf = NODEPTR(mp, 0);
        }

set1:
        mc->mc_flags |= C_INITIALIZED;
        mc->mc_flags &= ~C_EOF;

        if (IS_LEAF2(mp)) {
                key->mv_size = mc->mc_db->md_pad;
                key->mv_data = LEAF2KEY(mp, mc->mc_ki[mc->mc_top], key->mv_size);
                return MDB_SUCCESS;
        }

        if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
                mdb_xcursor_init1(mc, leaf);
        }
        if (data) {
                if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
                        if (op == MDB_SET || op == MDB_SET_KEY || op == MDB_SET_RANGE) {
                                rc = mdb_cursor_first(&mc->mc_xcursor->mx_cursor, data, NULL);
                        } else {
                                int ex2, *ex2p;
                                if (op == MDB_GET_BOTH) {
                                        ex2p = &ex2;
                                        ex2 = 0;
                                } else {
                                        ex2p = NULL;
                                }
                                rc = mdb_cursor_set(&mc->mc_xcursor->mx_cursor, data, NULL, MDB_SET_RANGE, ex2p);
                                if (rc != MDB_SUCCESS)
                                        return rc;
                        }
                } else if (op == MDB_GET_BOTH || op == MDB_GET_BOTH_RANGE) {
                        MDB_val d2;
                        if ((rc = mdb_node_read(mc->mc_txn, leaf, &d2)) != MDB_SUCCESS)
                                return rc;
                        rc = mc->mc_dbx->md_dcmp(data, &d2);
                        if (rc) {
                                if (op == MDB_GET_BOTH || rc > 0)
                                        return MDB_NOTFOUND;
                        }

                } else {
                        if (mc->mc_xcursor)
                                mc->mc_xcursor->mx_cursor.mc_flags &= ~(C_INITIALIZED|C_EOF);
                        if ((rc = mdb_node_read(mc->mc_txn, leaf, data)) != MDB_SUCCESS)
                                return rc;
                }
        }

        /* The key already matches in all other cases */
        if (op == MDB_SET_RANGE || op == MDB_SET_KEY)
                MDB_GET_KEY(leaf, key);
        DPRINTF("==> cursor placed on key [%s]", DKEY(key));

        return rc;
}

/** Move the cursor to the first item in the database. */
static int
mdb_cursor_first(MDB_cursor *mc, MDB_val *key, MDB_val *data)
{
        int              rc;
        MDB_node        *leaf;

        if (!(mc->mc_flags & C_INITIALIZED) || mc->mc_top) {
                rc = mdb_page_search(mc, NULL, 0);
                if (rc != MDB_SUCCESS)
                        return rc;
        }
        assert(IS_LEAF(mc->mc_pg[mc->mc_top]));

        leaf = NODEPTR(mc->mc_pg[mc->mc_top], 0);
        mc->mc_flags |= C_INITIALIZED;
        mc->mc_flags &= ~C_EOF;

        mc->mc_ki[mc->mc_top] = 0;

        if (IS_LEAF2(mc->mc_pg[mc->mc_top])) {
                key->mv_size = mc->mc_db->md_pad;
                key->mv_data = LEAF2KEY(mc->mc_pg[mc->mc_top], 0, key->mv_size);
                return MDB_SUCCESS;
        }

        if (data) {
                if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
                        mdb_xcursor_init1(mc, leaf);
                        rc = mdb_cursor_first(&mc->mc_xcursor->mx_cursor, data, NULL);
                        if (rc)
                                return rc;
                } else {
                        if (mc->mc_xcursor)
                                mc->mc_xcursor->mx_cursor.mc_flags &= ~(C_INITIALIZED|C_EOF);
                        if ((rc = mdb_node_read(mc->mc_txn, leaf, data)) != MDB_SUCCESS)
                                return rc;
                }
        }
        MDB_GET_KEY(leaf, key);
        return MDB_SUCCESS;
}

/** Move the cursor to the last item in the database. */
static int
mdb_cursor_last(MDB_cursor *mc, MDB_val *key, MDB_val *data)
{
        int              rc;
        MDB_node        *leaf;

        if (!(mc->mc_flags & C_EOF)) {

                if (!(mc->mc_flags & C_INITIALIZED) || mc->mc_top) {
                        MDB_val lkey;

                        lkey.mv_size = MDB_MAXKEYSIZE+1;
                        lkey.mv_data = NULL;
                        rc = mdb_page_search(mc, &lkey, 0);
                        if (rc != MDB_SUCCESS)
                                return rc;
                }
                assert(IS_LEAF(mc->mc_pg[mc->mc_top]));

        }
        mc->mc_ki[mc->mc_top] = NUMKEYS(mc->mc_pg[mc->mc_top]) - 1;
        mc->mc_flags |= C_INITIALIZED|C_EOF;
        leaf = NODEPTR(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);

        if (IS_LEAF2(mc->mc_pg[mc->mc_top])) {
                key->mv_size = mc->mc_db->md_pad;
                key->mv_data = LEAF2KEY(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top], key->mv_size);
                return MDB_SUCCESS;
        }

        if (data) {
                if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
                        mdb_xcursor_init1(mc, leaf);
                        rc = mdb_cursor_last(&mc->mc_xcursor->mx_cursor, data, NULL);
                        if (rc)
                                return rc;
                } else {
                        if (mc->mc_xcursor)
                                mc->mc_xcursor->mx_cursor.mc_flags &= ~(C_INITIALIZED|C_EOF);
                        if ((rc = mdb_node_read(mc->mc_txn, leaf, data)) != MDB_SUCCESS)
                                return rc;
                }
        }

        MDB_GET_KEY(leaf, key);
        return MDB_SUCCESS;
}

int
mdb_cursor_get(MDB_cursor *mc, MDB_val *key, MDB_val *data,
    MDB_cursor_op op)
{
        int              rc;
        int              exact = 0;

        assert(mc);

        switch (op) {
        case MDB_GET_CURRENT:
                if (!(mc->mc_flags & C_INITIALIZED)) {
                        rc = EINVAL;
                } else {
                        MDB_page *mp = mc->mc_pg[mc->mc_top];
                        if (!NUMKEYS(mp)) {
                                mc->mc_ki[mc->mc_top] = 0;
                                rc = MDB_NOTFOUND;
                                break;
                        }
                        rc = MDB_SUCCESS;
                        if (IS_LEAF2(mp)) {
                                key->mv_size = mc->mc_db->md_pad;
                                key->mv_data = LEAF2KEY(mp, mc->mc_ki[mc->mc_top], key->mv_size);
                        } else {
                                MDB_node *leaf = NODEPTR(mp, mc->mc_ki[mc->mc_top]);
                                MDB_GET_KEY(leaf, key);
                                if (data) {
                                        if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
                                                rc = mdb_cursor_get(&mc->mc_xcursor->mx_cursor, data, NULL, MDB_GET_CURRENT);
                                        } else {
                                                rc = mdb_node_read(mc->mc_txn, leaf, data);
                                        }
                                }
                        }
                }
                break;
        case MDB_GET_BOTH:
        case MDB_GET_BOTH_RANGE:
                if (data == NULL || mc->mc_xcursor == NULL) {
                        rc = EINVAL;
                        break;
                }
                /* FALLTHRU */
        case MDB_SET:
        case MDB_SET_KEY:
        case MDB_SET_RANGE:
                if (key == NULL || key->mv_size == 0 || key->mv_size > MDB_MAXKEYSIZE) {
                        rc = EINVAL;
                } else if (op == MDB_SET_RANGE)
                        rc = mdb_cursor_set(mc, key, data, op, NULL);
                else
                        rc = mdb_cursor_set(mc, key, data, op, &exact);
                break;
        case MDB_GET_MULTIPLE:
                if (data == NULL ||
                        !(mc->mc_db->md_flags & MDB_DUPFIXED) ||
                        !(mc->mc_flags & C_INITIALIZED)) {
                        rc = EINVAL;
                        break;
                }
                rc = MDB_SUCCESS;
                if (!(mc->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED) ||
                        (mc->mc_xcursor->mx_cursor.mc_flags & C_EOF))
                        break;
                goto fetchm;
        case MDB_NEXT_MULTIPLE:
                if (data == NULL ||
                        !(mc->mc_db->md_flags & MDB_DUPFIXED)) {
                        rc = EINVAL;
                        break;
                }
                if (!(mc->mc_flags & C_INITIALIZED))
                        rc = mdb_cursor_first(mc, key, data);
                else
                        rc = mdb_cursor_next(mc, key, data, MDB_NEXT_DUP);
                if (rc == MDB_SUCCESS) {
                        if (mc->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED) {
                                MDB_cursor *mx;
fetchm:
                                mx = &mc->mc_xcursor->mx_cursor;
                                data->mv_size = NUMKEYS(mx->mc_pg[mx->mc_top]) *
                                        mx->mc_db->md_pad;
                                data->mv_data = METADATA(mx->mc_pg[mx->mc_top]);
                                mx->mc_ki[mx->mc_top] = NUMKEYS(mx->mc_pg[mx->mc_top])-1;
                        } else {
                                rc = MDB_NOTFOUND;
                        }
                }
                break;
        case MDB_NEXT:
        case MDB_NEXT_DUP:
        case MDB_NEXT_NODUP:
                if (!(mc->mc_flags & C_INITIALIZED))
                        rc = mdb_cursor_first(mc, key, data);
                else
                        rc = mdb_cursor_next(mc, key, data, op);
                break;
        case MDB_PREV:
        case MDB_PREV_DUP:
        case MDB_PREV_NODUP:
                if (!(mc->mc_flags & C_INITIALIZED)) {
                        rc = mdb_cursor_last(mc, key, data);
                        if (rc)
                                break;
                        mc->mc_flags |= C_INITIALIZED;
                        mc->mc_ki[mc->mc_top]++;
                }
                rc = mdb_cursor_prev(mc, key, data, op);
                break;
        case MDB_FIRST:
                rc = mdb_cursor_first(mc, key, data);
                break;
        case MDB_FIRST_DUP:
                if (data == NULL ||
                        !(mc->mc_db->md_flags & MDB_DUPSORT) ||
                        !(mc->mc_flags & C_INITIALIZED) ||
                        !(mc->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED)) {
                        rc = EINVAL;
                        break;
                }
                rc = mdb_cursor_first(&mc->mc_xcursor->mx_cursor, data, NULL);
                break;
        case MDB_LAST:
                rc = mdb_cursor_last(mc, key, data);
                break;
        case MDB_LAST_DUP:
                if (data == NULL ||
                        !(mc->mc_db->md_flags & MDB_DUPSORT) ||
                        !(mc->mc_flags & C_INITIALIZED) ||
                        !(mc->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED)) {
                        rc = EINVAL;
                        break;
                }
                rc = mdb_cursor_last(&mc->mc_xcursor->mx_cursor, data, NULL);
                break;
        default:
                DPRINTF("unhandled/unimplemented cursor operation %u", op);
                rc = EINVAL;
                break;
        }

        return rc;
}

/** Touch all the pages in the cursor stack.
 *      Makes sure all the pages are writable, before attempting a write operation.
 * @param[in] mc The cursor to operate on.
 */
static int
mdb_cursor_touch(MDB_cursor *mc)
{
        int rc;

        if (mc->mc_dbi > MAIN_DBI && !(*mc->mc_dbflag & DB_DIRTY)) {
                MDB_cursor mc2;
                MDB_xcursor mcx;
                mdb_cursor_init(&mc2, mc->mc_txn, MAIN_DBI, &mcx);
                rc = mdb_page_search(&mc2, &mc->mc_dbx->md_name, MDB_PS_MODIFY);
                if (rc)
                         return rc;
                *mc->mc_dbflag |= DB_DIRTY;
        }
        for (mc->mc_top = 0; mc->mc_top < mc->mc_snum; mc->mc_top++) {
                rc = mdb_page_touch(mc);
                if (rc)
                        return rc;
        }
        mc->mc_top = mc->mc_snum-1;
        return MDB_SUCCESS;
}

/** Do not spill pages to disk if txn is getting full, may fail instead */
#define MDB_NOSPILL     0x8000

int
mdb_cursor_put(MDB_cursor *mc, MDB_val *key, MDB_val *data,
    unsigned int flags)
{
        enum { MDB_NO_ROOT = MDB_LAST_ERRCODE+10 }; /* internal code */
        MDB_node        *leaf = NULL;
        MDB_val xdata, *rdata, dkey;
        MDB_page        *fp;
        MDB_db dummy;
        int do_sub = 0, insert = 0;
        unsigned int mcount = 0, dcount = 0, nospill;
        size_t nsize;
        int rc, rc2;
        MDB_pagebuf pbuf;
        char dbuf[MDB_MAXKEYSIZE+1];
        unsigned int nflags;
        DKBUF;

        /* Check this first so counter will always be zero on any
         * early failures.
         */
        if (flags & MDB_MULTIPLE) {
                dcount = data[1].mv_size;
                data[1].mv_size = 0;
                if (!F_ISSET(mc->mc_db->md_flags, MDB_DUPFIXED))
                        return EINVAL;
        }

        nospill = flags & MDB_NOSPILL;
        flags &= ~MDB_NOSPILL;

        if (F_ISSET(mc->mc_txn->mt_flags, MDB_TXN_RDONLY))
                return EACCES;

        if (flags != MDB_CURRENT && (key->mv_size == 0 || key->mv_size > MDB_MAXKEYSIZE))
                return EINVAL;

        if (F_ISSET(mc->mc_db->md_flags, MDB_DUPSORT) && data->mv_size > MDB_MAXKEYSIZE)
                return EINVAL;

#if SIZE_MAX > MAXDATASIZE
        if (data->mv_size > MAXDATASIZE)
                return EINVAL;
#endif

        DPRINTF("==> put db %u key [%s], size %zu, data size %zu",
                mc->mc_dbi, DKEY(key), key ? key->mv_size:0, data->mv_size);

        dkey.mv_size = 0;

        if (flags == MDB_CURRENT) {
                if (!(mc->mc_flags & C_INITIALIZED))
                        return EINVAL;
                rc = MDB_SUCCESS;
        } else if (mc->mc_db->md_root == P_INVALID) {
                /* new database, cursor has nothing to point to */
                mc->mc_snum = 0;
                mc->mc_flags &= ~C_INITIALIZED;
                rc = MDB_NO_ROOT;
        } else {
                int exact = 0;
                MDB_val d2;
                if (flags & MDB_APPEND) {
                        MDB_val k2;
                        rc = mdb_cursor_last(mc, &k2, &d2);
                        if (rc == 0) {
                                rc = mc->mc_dbx->md_cmp(key, &k2);
                                if (rc > 0) {
                                        rc = MDB_NOTFOUND;
                                        mc->mc_ki[mc->mc_top]++;
                                } else {
                                        /* new key is <= last key */
                                        rc = MDB_KEYEXIST;
                                }
                        }
                } else {
                        rc = mdb_cursor_set(mc, key, &d2, MDB_SET, &exact);
                }
                if ((flags & MDB_NOOVERWRITE) && rc == 0) {
                        DPRINTF("duplicate key [%s]", DKEY(key));
                        *data = d2;
                        return MDB_KEYEXIST;
                }
                if (rc && rc != MDB_NOTFOUND)
                        return rc;
        }

        /* Cursor is positioned, check for room in the dirty list */
        if (!nospill) {
                if (flags & MDB_MULTIPLE) {
                        rdata = &xdata;
                        xdata.mv_size = data->mv_size * dcount;
                } else {
                        rdata = data;
                }
                if ((rc2 = mdb_page_spill(mc, key, rdata)))
                        return rc2;
        }

        if (rc == MDB_NO_ROOT) {
                MDB_page *np;
                /* new database, write a root leaf page */
                DPUTS("allocating new root leaf page");
                if ((rc2 = mdb_page_new(mc, P_LEAF, 1, &np))) {
                        return rc2;
                }
                mdb_cursor_push(mc, np);
                mc->mc_db->md_root = np->mp_pgno;
                mc->mc_db->md_depth++;
                *mc->mc_dbflag |= DB_DIRTY;
                if ((mc->mc_db->md_flags & (MDB_DUPSORT|MDB_DUPFIXED))
                        == MDB_DUPFIXED)
                        np->mp_flags |= P_LEAF2;
                mc->mc_flags |= C_INITIALIZED;
        } else {
                /* make sure all cursor pages are writable */
                rc2 = mdb_cursor_touch(mc);
                if (rc2)
                        return rc2;
        }

        /* The key already exists */
        if (rc == MDB_SUCCESS) {
                /* there's only a key anyway, so this is a no-op */
                if (IS_LEAF2(mc->mc_pg[mc->mc_top])) {
                        unsigned int ksize = mc->mc_db->md_pad;
                        if (key->mv_size != ksize)
                                return EINVAL;
                        if (flags == MDB_CURRENT) {
                                char *ptr = LEAF2KEY(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top], ksize);
                                memcpy(ptr, key->mv_data, ksize);
                        }
                        return MDB_SUCCESS;
                }

                leaf = NODEPTR(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);

                /* DB has dups? */
                if (F_ISSET(mc->mc_db->md_flags, MDB_DUPSORT)) {
                        /* Was a single item before, must convert now */
more:
                        if (!F_ISSET(leaf->mn_flags, F_DUPDATA)) {
                                /* Just overwrite the current item */
                                if (flags == MDB_CURRENT)
                                        goto current;

                                dkey.mv_size = NODEDSZ(leaf);
                                dkey.mv_data = NODEDATA(leaf);
#if UINT_MAX < SIZE_MAX
                                if (mc->mc_dbx->md_dcmp == mdb_cmp_int && dkey.mv_size == sizeof(size_t))
#ifdef MISALIGNED_OK
                                        mc->mc_dbx->md_dcmp = mdb_cmp_long;
#else
                                        mc->mc_dbx->md_dcmp = mdb_cmp_cint;
#endif
#endif
                                /* if data matches, ignore it */
                                if (!mc->mc_dbx->md_dcmp(data, &dkey))
                                        return (flags == MDB_NODUPDATA) ? MDB_KEYEXIST : MDB_SUCCESS;

                                /* create a fake page for the dup items */
                                memcpy(dbuf, dkey.mv_data, dkey.mv_size);
                                dkey.mv_data = dbuf;
                                fp = (MDB_page *)&pbuf;
                                fp->mp_pgno = mc->mc_pg[mc->mc_top]->mp_pgno;
                                fp->mp_flags = P_LEAF|P_DIRTY|P_SUBP;
                                fp->mp_lower = PAGEHDRSZ;
                                fp->mp_upper = PAGEHDRSZ + dkey.mv_size + data->mv_size;
                                if (mc->mc_db->md_flags & MDB_DUPFIXED) {
                                        fp->mp_flags |= P_LEAF2;
                                        fp->mp_pad = data->mv_size;
                                        fp->mp_upper += 2 * data->mv_size;      /* leave space for 2 more */
                                } else {
                                        fp->mp_upper += 2 * sizeof(indx_t) + 2 * NODESIZE +
                                                (dkey.mv_size & 1) + (data->mv_size & 1);
                                }
                                mdb_node_del(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top], 0);
                                do_sub = 1;
                                rdata = &xdata;
                                xdata.mv_size = fp->mp_upper;
                                xdata.mv_data = fp;
                                flags |= F_DUPDATA;
                                goto new_sub;
                        }
                        if (!F_ISSET(leaf->mn_flags, F_SUBDATA)) {
                                /* See if we need to convert from fake page to subDB */
                                MDB_page *mp;
                                unsigned int offset;
                                unsigned int i;
                                uint16_t fp_flags;

                                fp = NODEDATA(leaf);
                                if (flags == MDB_CURRENT) {
reuse:
                                        fp->mp_flags |= P_DIRTY;
                                        COPY_PGNO(fp->mp_pgno, mc->mc_pg[mc->mc_top]->mp_pgno);
                                        mc->mc_xcursor->mx_cursor.mc_pg[0] = fp;
                                        flags |= F_DUPDATA;
                                        goto put_sub;
                                }
                                if (mc->mc_db->md_flags & MDB_DUPFIXED) {
                                        offset = fp->mp_pad;
                                        if (SIZELEFT(fp) >= offset)
                                                goto reuse;
                                        offset *= 4;    /* space for 4 more */
                                } else {
                                        offset = NODESIZE + sizeof(indx_t) + data->mv_size;
                                }
                                offset += offset & 1;
                                fp_flags = fp->mp_flags;
                                if (NODESIZE + sizeof(indx_t) + NODEKSZ(leaf) + NODEDSZ(leaf) +
                                        offset >= mc->mc_txn->mt_env->me_nodemax) {
                                        /* yes, convert it */
                                        dummy.md_flags = 0;
                                        if (mc->mc_db->md_flags & MDB_DUPFIXED) {
                                                dummy.md_pad = fp->mp_pad;
                                                dummy.md_flags = MDB_DUPFIXED;
                                                if (mc->mc_db->md_flags & MDB_INTEGERDUP)
                                                        dummy.md_flags |= MDB_INTEGERKEY;
                                        }
                                        dummy.md_depth = 1;
                                        dummy.md_branch_pages = 0;
                                        dummy.md_leaf_pages = 1;
                                        dummy.md_overflow_pages = 0;
                                        dummy.md_entries = NUMKEYS(fp);
                                        rdata = &xdata;
                                        xdata.mv_size = sizeof(MDB_db);
                                        xdata.mv_data = &dummy;
                                        if ((rc = mdb_page_alloc(mc, 1, &mp)))
                                                return rc;
                                        offset = mc->mc_txn->mt_env->me_psize - NODEDSZ(leaf);
                                        flags |= F_DUPDATA|F_SUBDATA;
                                        dummy.md_root = mp->mp_pgno;
                                        fp_flags &= ~P_SUBP;
                                } else {
                                        /* no, just grow it */
                                        rdata = &xdata;
                                        xdata.mv_size = NODEDSZ(leaf) + offset;
                                        xdata.mv_data = &pbuf;
                                        mp = (MDB_page *)&pbuf;
                                        mp->mp_pgno = mc->mc_pg[mc->mc_top]->mp_pgno;
                                        flags |= F_DUPDATA;
                                }
                                mp->mp_flags = fp_flags | P_DIRTY;
                                mp->mp_pad   = fp->mp_pad;
                                mp->mp_lower = fp->mp_lower;
                                mp->mp_upper = fp->mp_upper + offset;
                                if (IS_LEAF2(fp)) {
                                        memcpy(METADATA(mp), METADATA(fp), NUMKEYS(fp) * fp->mp_pad);
                                } else {
                                        nsize = NODEDSZ(leaf) - fp->mp_upper;
                                        memcpy((char *)mp + mp->mp_upper, (char *)fp + fp->mp_upper, nsize);
                                        for (i=0; i<NUMKEYS(fp); i++)
                                                mp->mp_ptrs[i] = fp->mp_ptrs[i] + offset;
                                }
                                mdb_node_del(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top], 0);
                                do_sub = 1;
                                goto new_sub;
                        }
                        /* data is on sub-DB, just store it */
                        flags |= F_DUPDATA|F_SUBDATA;
                        goto put_sub;
                }
current:
                /* overflow page overwrites need special handling */
                if (F_ISSET(leaf->mn_flags, F_BIGDATA)) {
                        MDB_page *omp;
                        pgno_t pg;
                        unsigned psize = mc->mc_txn->mt_env->me_psize;
                        int level, ovpages, dpages = OVPAGES(data->mv_size, psize);

                        memcpy(&pg, NODEDATA(leaf), sizeof(pg));
                        if ((rc2 = mdb_page_get(mc->mc_txn, pg, &omp, &level)) != 0)
                                return rc2;
                        ovpages = omp->mp_pages;

                        /* Is the ov page large enough? */
                        if (ovpages >= dpages) {
                          if (!(omp->mp_flags & P_DIRTY) &&
                                  (level || (mc->mc_txn->mt_env->me_flags & MDB_WRITEMAP)))
                          {
                                rc = mdb_page_unspill(mc->mc_txn, omp, &omp);
                                if (rc)
                                        return rc;
                                level = 0;              /* dirty in this txn or clean */
                          }
                          /* Is it dirty? */
                          if (omp->mp_flags & P_DIRTY) {
                                /* yes, overwrite it. Note in this case we don't
                                 * bother to try shrinking the page if the new data
                                 * is smaller than the overflow threshold.
                                 */
                                if (level > 1) {
                                        /* It is writable only in a parent txn */
                                        size_t sz = (size_t) psize * ovpages, off;
                                        MDB_page *np = mdb_page_malloc(mc->mc_txn, ovpages);
                                        MDB_ID2 id2;
                                        if (!np)
                                                return ENOMEM;
                                        id2.mid = pg;
                                        id2.mptr = np;
                                        mdb_mid2l_insert(mc->mc_txn->mt_u.dirty_list, &id2);
                                        if (!(flags & MDB_RESERVE)) {
                                                /* Copy end of page, adjusting alignment so
                                                 * compiler may copy words instead of bytes.
                                                 */
                                                off = (PAGEHDRSZ + data->mv_size) & -sizeof(size_t);
                                                memcpy((size_t *)((char *)np + off),
                                                        (size_t *)((char *)omp + off), sz - off);
                                                sz = PAGEHDRSZ;
                                        }
                                        memcpy(np, omp, sz); /* Copy beginning of page */
                                        omp = np;
                                }
                                SETDSZ(leaf, data->mv_size);
                                if (F_ISSET(flags, MDB_RESERVE))
                                        data->mv_data = METADATA(omp);
                                else
                                        memcpy(METADATA(omp), data->mv_data, data->mv_size);
                                goto done;
                          }
                        }
                        if ((rc2 = mdb_ovpage_free(mc, omp)) != MDB_SUCCESS)
                                return rc2;
                } else if (NODEDSZ(leaf) == data->mv_size) {
                        /* same size, just replace it. Note that we could
                         * also reuse this node if the new data is smaller,
                         * but instead we opt to shrink the node in that case.
                         */
                        if (F_ISSET(flags, MDB_RESERVE))
                                data->mv_data = NODEDATA(leaf);
                        else if (data->mv_size)
                                memcpy(NODEDATA(leaf), data->mv_data, data->mv_size);
                        else
                                memcpy(NODEKEY(leaf), key->mv_data, key->mv_size);
                        goto done;
                }
                mdb_node_del(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top], 0);
                mc->mc_db->md_entries--;
        } else {
                DPRINTF("inserting key at index %i", mc->mc_ki[mc->mc_top]);
                insert = 1;
        }

        rdata = data;

new_sub:
        nflags = flags & NODE_ADD_FLAGS;
        nsize = IS_LEAF2(mc->mc_pg[mc->mc_top]) ? key->mv_size : mdb_leaf_size(mc->mc_txn->mt_env, key, rdata);
        if (SIZELEFT(mc->mc_pg[mc->mc_top]) < nsize) {
                if (( flags & (F_DUPDATA|F_SUBDATA)) == F_DUPDATA )
                        nflags &= ~MDB_APPEND;
                if (!insert)
                        nflags |= MDB_SPLIT_REPLACE;
                rc = mdb_page_split(mc, key, rdata, P_INVALID, nflags);
        } else {
                /* There is room already in this leaf page. */
                rc = mdb_node_add(mc, mc->mc_ki[mc->mc_top], key, rdata, 0, nflags);
                if (rc == 0 && !do_sub && insert) {
                        /* Adjust other cursors pointing to mp */
                        MDB_cursor *m2, *m3;
                        MDB_dbi dbi = mc->mc_dbi;
                        unsigned i = mc->mc_top;
                        MDB_page *mp = mc->mc_pg[i];

                        if (mc->mc_flags & C_SUB)
                                dbi--;

                        for (m2 = mc->mc_txn->mt_cursors[dbi]; m2; m2=m2->mc_next) {
                                if (mc->mc_flags & C_SUB)
                                        m3 = &m2->mc_xcursor->mx_cursor;
                                else
                                        m3 = m2;
                                if (m3 == mc || m3->mc_snum < mc->mc_snum) continue;
                                if (m3->mc_pg[i] == mp && m3->mc_ki[i] >= mc->mc_ki[i]) {
                                        m3->mc_ki[i]++;
                                }
                        }
                }
        }

        if (rc != MDB_SUCCESS)
                mc->mc_txn->mt_flags |= MDB_TXN_ERROR;
        else {
                /* Now store the actual data in the child DB. Note that we're
                 * storing the user data in the keys field, so there are strict
                 * size limits on dupdata. The actual data fields of the child
                 * DB are all zero size.
                 */
                if (do_sub) {
                        int xflags;
put_sub:
                        xdata.mv_size = 0;
                        xdata.mv_data = "";
                        leaf = NODEPTR(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);
                        if (flags & MDB_CURRENT) {
                                xflags = MDB_CURRENT|MDB_NOSPILL;
                        } else {
                                mdb_xcursor_init1(mc, leaf);
                                xflags = (flags & MDB_NODUPDATA) ?
                                        MDB_NOOVERWRITE|MDB_NOSPILL : MDB_NOSPILL;
                        }
                        /* converted, write the original data first */
                        if (dkey.mv_size) {
                                rc = mdb_cursor_put(&mc->mc_xcursor->mx_cursor, &dkey, &xdata, xflags);
                                if (rc)
                                        return rc;
                                {
                                        /* Adjust other cursors pointing to mp */
                                        MDB_cursor *m2;
                                        unsigned i = mc->mc_top;
                                        MDB_page *mp = mc->mc_pg[i];

                                        for (m2 = mc->mc_txn->mt_cursors[mc->mc_dbi]; m2; m2=m2->mc_next) {
                                                if (m2 == mc || m2->mc_snum < mc->mc_snum) continue;
                                                if (!(m2->mc_flags & C_INITIALIZED)) continue;
                                                if (m2->mc_pg[i] == mp && m2->mc_ki[i] == mc->mc_ki[i]) {
                                                        mdb_xcursor_init1(m2, leaf);
                                                }
                                        }
                                }
                                /* we've done our job */
                                dkey.mv_size = 0;
                        }
                        if (flags & MDB_APPENDDUP)
                                xflags |= MDB_APPEND;
                        rc = mdb_cursor_put(&mc->mc_xcursor->mx_cursor, data, &xdata, xflags);
                        if (flags & F_SUBDATA) {
                                void *db = NODEDATA(leaf);
                                memcpy(db, &mc->mc_xcursor->mx_db, sizeof(MDB_db));
                        }
                }
                /* sub-writes might have failed so check rc again.
                 * Don't increment count if we just replaced an existing item.
                 */
                if (!rc && !(flags & MDB_CURRENT))
                        mc->mc_db->md_entries++;
                if (flags & MDB_MULTIPLE) {
                        if (!rc) {
                                mcount++;
                                if (mcount < dcount) {
                                        data[0].mv_data = (char *)data[0].mv_data + data[0].mv_size;
                                        leaf = NODEPTR(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);
                                        goto more;
                                }
                        }
                        /* let caller know how many succeeded, if any */
                        data[1].mv_size = mcount;
                }
        }
done:
        /* If we succeeded and the key didn't exist before, make sure
         * the cursor is marked valid.
         */
        if (!rc && insert)
                mc->mc_flags |= C_INITIALIZED;
        return rc;
}

int
mdb_cursor_del(MDB_cursor *mc, unsigned int flags)
{
        MDB_node        *leaf;
        int rc;

        if (F_ISSET(mc->mc_txn->mt_flags, MDB_TXN_RDONLY))
                return EACCES;

        if (!(mc->mc_flags & C_INITIALIZED))
                return EINVAL;

        if (!(flags & MDB_NOSPILL) && (rc = mdb_page_spill(mc, NULL, NULL)))
                return rc;
        flags &= ~MDB_NOSPILL; /* TODO: Or change (flags != MDB_NODUPDATA) to ~(flags & MDB_NODUPDATA), not looking at the logic of that code just now */

        rc = mdb_cursor_touch(mc);
        if (rc)
                return rc;

        leaf = NODEPTR(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);

        if (!IS_LEAF2(mc->mc_pg[mc->mc_top]) && F_ISSET(leaf->mn_flags, F_DUPDATA)) {
                if (flags != MDB_NODUPDATA) {
                        if (!F_ISSET(leaf->mn_flags, F_SUBDATA)) {
                                mc->mc_xcursor->mx_cursor.mc_pg[0] = NODEDATA(leaf);
                        }
                        rc = mdb_cursor_del(&mc->mc_xcursor->mx_cursor, MDB_NOSPILL);
                        /* If sub-DB still has entries, we're done */
                        if (mc->mc_xcursor->mx_db.md_entries) {
                                if (leaf->mn_flags & F_SUBDATA) {
                                        /* update subDB info */
                                        void *db = NODEDATA(leaf);
                                        memcpy(db, &mc->mc_xcursor->mx_db, sizeof(MDB_db));
                                } else {
                                        MDB_cursor *m2;
                                        /* shrink fake page */
                                        mdb_node_shrink(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);
                                        leaf = NODEPTR(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);
                                        mc->mc_xcursor->mx_cursor.mc_pg[0] = NODEDATA(leaf);
                                        /* fix other sub-DB cursors pointed at this fake page */
                                        for (m2 = mc->mc_txn->mt_cursors[mc->mc_dbi]; m2; m2=m2->mc_next) {
                                                if (m2 == mc || m2->mc_snum < mc->mc_snum) continue;
                                                if (m2->mc_pg[mc->mc_top] == mc->mc_pg[mc->mc_top] &&
                                                        m2->mc_ki[mc->mc_top] == mc->mc_ki[mc->mc_top])
                                                        m2->mc_xcursor->mx_cursor.mc_pg[0] = NODEDATA(leaf);
                                        }
                                }
                                mc->mc_db->md_entries--;
                                return rc;
                        }
                        /* otherwise fall thru and delete the sub-DB */
                }

                if (leaf->mn_flags & F_SUBDATA) {
                        /* add all the child DB's pages to the free list */
                        rc = mdb_drop0(&mc->mc_xcursor->mx_cursor, 0);
                        if (rc == MDB_SUCCESS) {
                                mc->mc_db->md_entries -=
                                        mc->mc_xcursor->mx_db.md_entries;
                        }
                }
        }

        return mdb_cursor_del0(mc, leaf);
}

/** Allocate and initialize new pages for a database.
 * @param[in] mc a cursor on the database being added to.
 * @param[in] flags flags defining what type of page is being allocated.
 * @param[in] num the number of pages to allocate. This is usually 1,
 * unless allocating overflow pages for a large record.
 * @param[out] mp Address of a page, or NULL on failure.
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_page_new(MDB_cursor *mc, uint32_t flags, int num, MDB_page **mp)
{
        MDB_page        *np;
        int rc;

        if ((rc = mdb_page_alloc(mc, num, &np)))
                return rc;
        DPRINTF("allocated new mpage %zu, page size %u",
            np->mp_pgno, mc->mc_txn->mt_env->me_psize);
        np->mp_flags = flags | P_DIRTY;
        np->mp_lower = PAGEHDRSZ;
        np->mp_upper = mc->mc_txn->mt_env->me_psize;

        if (IS_BRANCH(np))
                mc->mc_db->md_branch_pages++;
        else if (IS_LEAF(np))
                mc->mc_db->md_leaf_pages++;
        else if (IS_OVERFLOW(np)) {
                mc->mc_db->md_overflow_pages += num;
                np->mp_pages = num;
        }
        *mp = np;

        return 0;
}

/** Calculate the size of a leaf node.
 * The size depends on the environment's page size; if a data item
 * is too large it will be put onto an overflow page and the node
 * size will only include the key and not the data. Sizes are always
 * rounded up to an even number of bytes, to guarantee 2-byte alignment
 * of the #MDB_node headers.
 * @param[in] env The environment handle.
 * @param[in] key The key for the node.
 * @param[in] data The data for the node.
 * @return The number of bytes needed to store the node.
 */
static size_t
mdb_leaf_size(MDB_env *env, MDB_val *key, MDB_val *data)
{
        size_t           sz;

        sz = LEAFSIZE(key, data);
        if (sz >= env->me_nodemax) {
                /* put on overflow page */
                sz -= data->mv_size - sizeof(pgno_t);
        }
        sz += sz & 1;

        return sz + sizeof(indx_t);
}

/** Calculate the size of a branch node.
 * The size should depend on the environment's page size but since
 * we currently don't support spilling large keys onto overflow
 * pages, it's simply the size of the #MDB_node header plus the
 * size of the key. Sizes are always rounded up to an even number
 * of bytes, to guarantee 2-byte alignment of the #MDB_node headers.
 * @param[in] env The environment handle.
 * @param[in] key The key for the node.
 * @return The number of bytes needed to store the node.
 */
static size_t
mdb_branch_size(MDB_env *env, MDB_val *key)
{
        size_t           sz;

        sz = INDXSIZE(key);
        if (sz >= env->me_nodemax) {
                /* put on overflow page */
                /* not implemented */
                /* sz -= key->size - sizeof(pgno_t); */
        }

        return sz + sizeof(indx_t);
}

/** Add a node to the page pointed to by the cursor.
 * @param[in] mc The cursor for this operation.
 * @param[in] indx The index on the page where the new node should be added.
 * @param[in] key The key for the new node.
 * @param[in] data The data for the new node, if any.
 * @param[in] pgno The page number, if adding a branch node.
 * @param[in] flags Flags for the node.
 * @return 0 on success, non-zero on failure. Possible errors are:
 * <ul>
 *      <li>ENOMEM - failed to allocate overflow pages for the node.
 *      <li>MDB_PAGE_FULL - there is insufficient room in the page. This error
 *      should never happen since all callers already calculate the
 *      page's free space before calling this function.
 * </ul>
 */
static int
mdb_node_add(MDB_cursor *mc, indx_t indx,
    MDB_val *key, MDB_val *data, pgno_t pgno, unsigned int flags)
{
        unsigned int     i;
        size_t           node_size = NODESIZE;
        indx_t           ofs;
        MDB_node        *node;
        MDB_page        *mp = mc->mc_pg[mc->mc_top];
        MDB_page        *ofp = NULL;            /* overflow page */
        DKBUF;

        assert(mp->mp_upper >= mp->mp_lower);

        DPRINTF("add to %s %spage %zu index %i, data size %zu key size %zu [%s]",
            IS_LEAF(mp) ? "leaf" : "branch",
                IS_SUBP(mp) ? "sub-" : "",
            mp->mp_pgno, indx, data ? data->mv_size : 0,
                key ? key->mv_size : 0, key ? DKEY(key) : NULL);

        if (IS_LEAF2(mp)) {
                /* Move higher keys up one slot. */
                int ksize = mc->mc_db->md_pad, dif;
                char *ptr = LEAF2KEY(mp, indx, ksize);
                dif = NUMKEYS(mp) - indx;
                if (dif > 0)
                        memmove(ptr+ksize, ptr, dif*ksize);
                /* insert new key */
                memcpy(ptr, key->mv_data, ksize);

                /* Just using these for counting */
                mp->mp_lower += sizeof(indx_t);
                mp->mp_upper -= ksize - sizeof(indx_t);
                return MDB_SUCCESS;
        }

        if (key != NULL)
                node_size += key->mv_size;

        if (IS_LEAF(mp)) {
                assert(data);
                if (F_ISSET(flags, F_BIGDATA)) {
                        /* Data already on overflow page. */
                        node_size += sizeof(pgno_t);
                } else if (node_size + data->mv_size >= mc->mc_txn->mt_env->me_nodemax) {
                        int ovpages = OVPAGES(data->mv_size, mc->mc_txn->mt_env->me_psize);
                        int rc;
                        /* Put data on overflow page. */
                        DPRINTF("data size is %zu, node would be %zu, put data on overflow page",
                            data->mv_size, node_size+data->mv_size);
                        node_size += sizeof(pgno_t);
                        if ((rc = mdb_page_new(mc, P_OVERFLOW, ovpages, &ofp)))
                                return rc;
                        DPRINTF("allocated overflow page %zu", ofp->mp_pgno);
                        flags |= F_BIGDATA;
                } else {
                        node_size += data->mv_size;
                }
        }
        node_size += node_size & 1;

        if (node_size + sizeof(indx_t) > SIZELEFT(mp)) {
                DPRINTF("not enough room in page %zu, got %u ptrs",
                    mp->mp_pgno, NUMKEYS(mp));
                DPRINTF("upper - lower = %u - %u = %u", mp->mp_upper, mp->mp_lower,
                    mp->mp_upper - mp->mp_lower);
                DPRINTF("node size = %zu", node_size);
                return MDB_PAGE_FULL;
        }

        /* Move higher pointers up one slot. */
        for (i = NUMKEYS(mp); i > indx; i--)
                mp->mp_ptrs[i] = mp->mp_ptrs[i - 1];

        /* Adjust free space offsets. */
        ofs = mp->mp_upper - node_size;
        assert(ofs >= mp->mp_lower + sizeof(indx_t));
        mp->mp_ptrs[indx] = ofs;
        mp->mp_upper = ofs;
        mp->mp_lower += sizeof(indx_t);

        /* Write the node data. */
        node = NODEPTR(mp, indx);
        node->mn_ksize = (key == NULL) ? 0 : key->mv_size;
        node->mn_flags = flags;
        if (IS_LEAF(mp))
                SETDSZ(node,data->mv_size);
        else
                SETPGNO(node,pgno);

        if (key)
                memcpy(NODEKEY(node), key->mv_data, key->mv_size);

        if (IS_LEAF(mp)) {
                assert(key);
                if (ofp == NULL) {
                        if (F_ISSET(flags, F_BIGDATA))
                                memcpy(node->mn_data + key->mv_size, data->mv_data,
                                    sizeof(pgno_t));
                        else if (F_ISSET(flags, MDB_RESERVE))
                                data->mv_data = node->mn_data + key->mv_size;
                        else
                                memcpy(node->mn_data + key->mv_size, data->mv_data,
                                    data->mv_size);
                } else {
                        memcpy(node->mn_data + key->mv_size, &ofp->mp_pgno,
                            sizeof(pgno_t));
                        if (F_ISSET(flags, MDB_RESERVE))
                                data->mv_data = METADATA(ofp);
                        else
                                memcpy(METADATA(ofp), data->mv_data, data->mv_size);
                }
        }

        return MDB_SUCCESS;
}

/** Delete the specified node from a page.
 * @param[in] mp The page to operate on.
 * @param[in] indx The index of the node to delete.
 * @param[in] ksize The size of a node. Only used if the page is
 * part of a #MDB_DUPFIXED database.
 */
static void
mdb_node_del(MDB_page *mp, indx_t indx, int ksize)
{
        unsigned int     sz;
        indx_t           i, j, numkeys, ptr;
        MDB_node        *node;
        char            *base;

#if MDB_DEBUG
        {
        pgno_t pgno;
        COPY_PGNO(pgno, mp->mp_pgno);
        DPRINTF("delete node %u on %s page %zu", indx,
            IS_LEAF(mp) ? "leaf" : "branch", pgno);
        }
#endif
        assert(indx < NUMKEYS(mp));

        if (IS_LEAF2(mp)) {
                int x = NUMKEYS(mp) - 1 - indx;
                base = LEAF2KEY(mp, indx, ksize);
                if (x)
                        memmove(base, base + ksize, x * ksize);
                mp->mp_lower -= sizeof(indx_t);
                mp->mp_upper += ksize - sizeof(indx_t);
                return;
        }

        node = NODEPTR(mp, indx);
        sz = NODESIZE + node->mn_ksize;
        if (IS_LEAF(mp)) {
                if (F_ISSET(node->mn_flags, F_BIGDATA))
                        sz += sizeof(pgno_t);
                else
                        sz += NODEDSZ(node);
        }
        sz += sz & 1;

        ptr = mp->mp_ptrs[indx];
        numkeys = NUMKEYS(mp);
        for (i = j = 0; i < numkeys; i++) {
                if (i != indx) {
                        mp->mp_ptrs[j] = mp->mp_ptrs[i];
                        if (mp->mp_ptrs[i] < ptr)
                                mp->mp_ptrs[j] += sz;
                        j++;
                }
        }

        base = (char *)mp + mp->mp_upper;
        memmove(base + sz, base, ptr - mp->mp_upper);

        mp->mp_lower -= sizeof(indx_t);
        mp->mp_upper += sz;
}

/** Compact the main page after deleting a node on a subpage.
 * @param[in] mp The main page to operate on.
 * @param[in] indx The index of the subpage on the main page.
 */
static void
mdb_node_shrink(MDB_page *mp, indx_t indx)
{
        MDB_node *node;
        MDB_page *sp, *xp;
        char *base;
        int osize, nsize;
        int delta;
        indx_t           i, numkeys, ptr;

        node = NODEPTR(mp, indx);
        sp = (MDB_page *)NODEDATA(node);
        osize = NODEDSZ(node);

        delta = sp->mp_upper - sp->mp_lower;
        SETDSZ(node, osize - delta);
        xp = (MDB_page *)((char *)sp + delta);

        /* shift subpage upward */
        if (IS_LEAF2(sp)) {
                nsize = NUMKEYS(sp) * sp->mp_pad;
                memmove(METADATA(xp), METADATA(sp), nsize);
        } else {
                int i;
                nsize = osize - sp->mp_upper;
                numkeys = NUMKEYS(sp);
                for (i=numkeys-1; i>=0; i--)
                        xp->mp_ptrs[i] = sp->mp_ptrs[i] - delta;
        }
        xp->mp_upper = sp->mp_lower;
        xp->mp_lower = sp->mp_lower;
        xp->mp_flags = sp->mp_flags;
        xp->mp_pad = sp->mp_pad;
        COPY_PGNO(xp->mp_pgno, mp->mp_pgno);

        /* shift lower nodes upward */
        ptr = mp->mp_ptrs[indx];
        numkeys = NUMKEYS(mp);
        for (i = 0; i < numkeys; i++) {
                if (mp->mp_ptrs[i] <= ptr)
                        mp->mp_ptrs[i] += delta;
        }

        base = (char *)mp + mp->mp_upper;
        memmove(base + delta, base, ptr - mp->mp_upper + NODESIZE + NODEKSZ(node));
        mp->mp_upper += delta;
}

/** Initial setup of a sorted-dups cursor.
 * Sorted duplicates are implemented as a sub-database for the given key.
 * The duplicate data items are actually keys of the sub-database.
 * Operations on the duplicate data items are performed using a sub-cursor
 * initialized when the sub-database is first accessed. This function does
 * the preliminary setup of the sub-cursor, filling in the fields that
 * depend only on the parent DB.
 * @param[in] mc The main cursor whose sorted-dups cursor is to be initialized.
 */
static void
mdb_xcursor_init0(MDB_cursor *mc)
{
        MDB_xcursor *mx = mc->mc_xcursor;

        mx->mx_cursor.mc_xcursor = NULL;
        mx->mx_cursor.mc_txn = mc->mc_txn;
        mx->mx_cursor.mc_db = &mx->mx_db;
        mx->mx_cursor.mc_dbx = &mx->mx_dbx;
        mx->mx_cursor.mc_dbi = mc->mc_dbi+1;
        mx->mx_cursor.mc_dbflag = &mx->mx_dbflag;
        mx->mx_cursor.mc_snum = 0;
        mx->mx_cursor.mc_top = 0;
        mx->mx_cursor.mc_flags = C_SUB;
        mx->mx_dbx.md_cmp = mc->mc_dbx->md_dcmp;
        mx->mx_dbx.md_dcmp = NULL;
        mx->mx_dbx.md_rel = mc->mc_dbx->md_rel;
}

/** Final setup of a sorted-dups cursor.
 *      Sets up the fields that depend on the data from the main cursor.
 * @param[in] mc The main cursor whose sorted-dups cursor is to be initialized.
 * @param[in] node The data containing the #MDB_db record for the
 * sorted-dup database.
 */
static void
mdb_xcursor_init1(MDB_cursor *mc, MDB_node *node)
{
        MDB_xcursor *mx = mc->mc_xcursor;

        if (node->mn_flags & F_SUBDATA) {
                memcpy(&mx->mx_db, NODEDATA(node), sizeof(MDB_db));
                mx->mx_cursor.mc_pg[0] = 0;
                mx->mx_cursor.mc_snum = 0;
                mx->mx_cursor.mc_flags = C_SUB;
        } else {
                MDB_page *fp = NODEDATA(node);
                mx->mx_db.md_pad = mc->mc_pg[mc->mc_top]->mp_pad;
                mx->mx_db.md_flags = 0;
                mx->mx_db.md_depth = 1;
                mx->mx_db.md_branch_pages = 0;
                mx->mx_db.md_leaf_pages = 1;
                mx->mx_db.md_overflow_pages = 0;
                mx->mx_db.md_entries = NUMKEYS(fp);
                COPY_PGNO(mx->mx_db.md_root, fp->mp_pgno);
                mx->mx_cursor.mc_snum = 1;
                mx->mx_cursor.mc_flags = C_INITIALIZED|C_SUB;
                mx->mx_cursor.mc_top = 0;
                mx->mx_cursor.mc_pg[0] = fp;
                mx->mx_cursor.mc_ki[0] = 0;
                if (mc->mc_db->md_flags & MDB_DUPFIXED) {
                        mx->mx_db.md_flags = MDB_DUPFIXED;
                        mx->mx_db.md_pad = fp->mp_pad;
                        if (mc->mc_db->md_flags & MDB_INTEGERDUP)
                                mx->mx_db.md_flags |= MDB_INTEGERKEY;
                }
        }
        DPRINTF("Sub-db %u for db %u root page %zu", mx->mx_cursor.mc_dbi, mc->mc_dbi,
                mx->mx_db.md_root);
        mx->mx_dbflag = DB_VALID | (F_ISSET(mc->mc_pg[mc->mc_top]->mp_flags, P_DIRTY) ?
                DB_DIRTY : 0);
        mx->mx_dbx.md_name.mv_data = NODEKEY(node);
        mx->mx_dbx.md_name.mv_size = node->mn_ksize;
#if UINT_MAX < SIZE_MAX
        if (mx->mx_dbx.md_cmp == mdb_cmp_int && mx->mx_db.md_pad == sizeof(size_t))
#ifdef MISALIGNED_OK
                mx->mx_dbx.md_cmp = mdb_cmp_long;
#else
                mx->mx_dbx.md_cmp = mdb_cmp_cint;
#endif
#endif
}

/** Initialize a cursor for a given transaction and database. */
static void
mdb_cursor_init(MDB_cursor *mc, MDB_txn *txn, MDB_dbi dbi, MDB_xcursor *mx)
{
        mc->mc_next = NULL;
        mc->mc_backup = NULL;
        mc->mc_dbi = dbi;
        mc->mc_txn = txn;
        mc->mc_db = &txn->mt_dbs[dbi];
        mc->mc_dbx = &txn->mt_dbxs[dbi];
        mc->mc_dbflag = &txn->mt_dbflags[dbi];
        mc->mc_snum = 0;
        mc->mc_top = 0;
        mc->mc_pg[0] = 0;
        mc->mc_flags = 0;
        if (txn->mt_dbs[dbi].md_flags & MDB_DUPSORT) {
                assert(mx != NULL);
                mc->mc_xcursor = mx;
                mdb_xcursor_init0(mc);
        } else {
                mc->mc_xcursor = NULL;
        }
        if (*mc->mc_dbflag & DB_STALE) {
                mdb_page_search(mc, NULL, MDB_PS_ROOTONLY);
        }
}

int
mdb_cursor_open(MDB_txn *txn, MDB_dbi dbi, MDB_cursor **ret)
{
        MDB_cursor      *mc;
        size_t size = sizeof(MDB_cursor);

        if (txn == NULL || ret == NULL || dbi >= txn->mt_numdbs || !(txn->mt_dbflags[dbi] & DB_VALID))
                return EINVAL;

        /* Allow read access to the freelist */
        if (!dbi && !F_ISSET(txn->mt_flags, MDB_TXN_RDONLY))
                return EINVAL;

        if (txn->mt_dbs[dbi].md_flags & MDB_DUPSORT)
                size += sizeof(MDB_xcursor);

        if ((mc = malloc(size)) != NULL) {
                mdb_cursor_init(mc, txn, dbi, (MDB_xcursor *)(mc + 1));
                if (txn->mt_cursors) {
                        mc->mc_next = txn->mt_cursors[dbi];
                        txn->mt_cursors[dbi] = mc;
                        mc->mc_flags |= C_UNTRACK;
                }
        } else {
                return ENOMEM;
        }

        *ret = mc;

        return MDB_SUCCESS;
}

int
mdb_cursor_renew(MDB_txn *txn, MDB_cursor *mc)
{
        if (txn == NULL || mc == NULL || mc->mc_dbi >= txn->mt_numdbs)
                return EINVAL;

        if ((mc->mc_flags & C_UNTRACK) || txn->mt_cursors)
                return EINVAL;

        mdb_cursor_init(mc, txn, mc->mc_dbi, mc->mc_xcursor);
        return MDB_SUCCESS;
}

/* Return the count of duplicate data items for the current key */
int
mdb_cursor_count(MDB_cursor *mc, size_t *countp)
{
        MDB_node        *leaf;

        if (mc == NULL || countp == NULL)
                return EINVAL;

        if (!(mc->mc_db->md_flags & MDB_DUPSORT))
                return EINVAL;

        leaf = NODEPTR(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);
        if (!F_ISSET(leaf->mn_flags, F_DUPDATA)) {
                *countp = 1;
        } else {
                if (!(mc->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED))
                        return EINVAL;

                *countp = mc->mc_xcursor->mx_db.md_entries;
        }
        return MDB_SUCCESS;
}

void
mdb_cursor_close(MDB_cursor *mc)
{
        if (mc && !mc->mc_backup) {
                /* remove from txn, if tracked */
                if ((mc->mc_flags & C_UNTRACK) && mc->mc_txn->mt_cursors) {
                        MDB_cursor **prev = &mc->mc_txn->mt_cursors[mc->mc_dbi];
                        while (*prev && *prev != mc) prev = &(*prev)->mc_next;
                        if (*prev == mc)
                                *prev = mc->mc_next;
                }
                free(mc);
        }
}

MDB_txn *
mdb_cursor_txn(MDB_cursor *mc)
{
        if (!mc) return NULL;
        return mc->mc_txn;
}

MDB_dbi
mdb_cursor_dbi(MDB_cursor *mc)
{
        assert(mc != NULL);
        return mc->mc_dbi;
}

/** Replace the key for a node with a new key.
 * @param[in] mc Cursor pointing to the node to operate on.
 * @param[in] key The new key to use.
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_update_key(MDB_cursor *mc, MDB_val *key)
{
        MDB_page                *mp;
        MDB_node                *node;
        char                    *base;
        size_t                   len;
        int                      delta, delta0;
        indx_t                   ptr, i, numkeys, indx;
        DKBUF;

        indx = mc->mc_ki[mc->mc_top];
        mp = mc->mc_pg[mc->mc_top];
        node = NODEPTR(mp, indx);
        ptr = mp->mp_ptrs[indx];
#if MDB_DEBUG
        {
                MDB_val k2;
                char kbuf2[(MDB_MAXKEYSIZE*2+1)];
                k2.mv_data = NODEKEY(node);
                k2.mv_size = node->mn_ksize;
                DPRINTF("update key %u (ofs %u) [%s] to [%s] on page %zu",
                        indx, ptr,
                        mdb_dkey(&k2, kbuf2),
                        DKEY(key),
                        mp->mp_pgno);
        }
#endif

        delta0 = delta = key->mv_size - node->mn_ksize;

        /* Must be 2-byte aligned. If new key is
         * shorter by 1, the shift will be skipped.
         */
        delta += (delta & 1);
        if (delta) {
                if (delta > 0 && SIZELEFT(mp) < delta) {
                        pgno_t pgno;
                        /* not enough space left, do a delete and split */
                        DPRINTF("Not enough room, delta = %d, splitting...", delta);
                        pgno = NODEPGNO(node);
                        mdb_node_del(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top], 0);
                        return mdb_page_split(mc, key, NULL, pgno, MDB_SPLIT_REPLACE);
                }

                numkeys = NUMKEYS(mp);
                for (i = 0; i < numkeys; i++) {
                        if (mp->mp_ptrs[i] <= ptr)
                                mp->mp_ptrs[i] -= delta;
                }

                base = (char *)mp + mp->mp_upper;
                len = ptr - mp->mp_upper + NODESIZE;
                memmove(base - delta, base, len);
                mp->mp_upper -= delta;

                node = NODEPTR(mp, indx);
        }

        /* But even if no shift was needed, update ksize */
        if (delta0)
                node->mn_ksize = key->mv_size;

        if (key->mv_size)
                memcpy(NODEKEY(node), key->mv_data, key->mv_size);

        return MDB_SUCCESS;
}

static void
mdb_cursor_copy(const MDB_cursor *csrc, MDB_cursor *cdst);

/** Move a node from csrc to cdst.
 */
static int
mdb_node_move(MDB_cursor *csrc, MDB_cursor *cdst)
{
        MDB_node                *srcnode;
        MDB_val          key, data;
        pgno_t  srcpg;
        MDB_cursor mn;
        int                      rc;
        unsigned short flags;

        DKBUF;

        /* Mark src and dst as dirty. */
        if ((rc = mdb_page_touch(csrc)) ||
            (rc = mdb_page_touch(cdst)))
                return rc;

        if (IS_LEAF2(csrc->mc_pg[csrc->mc_top])) {
                srcnode = NODEPTR(csrc->mc_pg[csrc->mc_top], 0);        /* fake */
                key.mv_size = csrc->mc_db->md_pad;
                key.mv_data = LEAF2KEY(csrc->mc_pg[csrc->mc_top], csrc->mc_ki[csrc->mc_top], key.mv_size);
                data.mv_size = 0;
                data.mv_data = NULL;
                srcpg = 0;
                flags = 0;
        } else {
                srcnode = NODEPTR(csrc->mc_pg[csrc->mc_top], csrc->mc_ki[csrc->mc_top]);
                assert(!((long)srcnode&1));
                srcpg = NODEPGNO(srcnode);
                flags = srcnode->mn_flags;
                if (csrc->mc_ki[csrc->mc_top] == 0 && IS_BRANCH(csrc->mc_pg[csrc->mc_top])) {
                        unsigned int snum = csrc->mc_snum;
                        MDB_node *s2;
                        /* must find the lowest key below src */
                        mdb_page_search_lowest(csrc);
                        if (IS_LEAF2(csrc->mc_pg[csrc->mc_top])) {
                                key.mv_size = csrc->mc_db->md_pad;
                                key.mv_data = LEAF2KEY(csrc->mc_pg[csrc->mc_top], 0, key.mv_size);
                        } else {
                                s2 = NODEPTR(csrc->mc_pg[csrc->mc_top], 0);
                                key.mv_size = NODEKSZ(s2);
                                key.mv_data = NODEKEY(s2);
                        }
                        csrc->mc_snum = snum--;
                        csrc->mc_top = snum;
                } else {
                        key.mv_size = NODEKSZ(srcnode);
                        key.mv_data = NODEKEY(srcnode);
                }
                data.mv_size = NODEDSZ(srcnode);
                data.mv_data = NODEDATA(srcnode);
        }
        if (IS_BRANCH(cdst->mc_pg[cdst->mc_top]) && cdst->mc_ki[cdst->mc_top] == 0) {
                unsigned int snum = cdst->mc_snum;
                MDB_node *s2;
                MDB_val bkey;
                /* must find the lowest key below dst */
                mdb_page_search_lowest(cdst);
                if (IS_LEAF2(cdst->mc_pg[cdst->mc_top])) {
                        bkey.mv_size = cdst->mc_db->md_pad;
                        bkey.mv_data = LEAF2KEY(cdst->mc_pg[cdst->mc_top], 0, bkey.mv_size);
                } else {
                        s2 = NODEPTR(cdst->mc_pg[cdst->mc_top], 0);
                        bkey.mv_size = NODEKSZ(s2);
                        bkey.mv_data = NODEKEY(s2);
                }
                cdst->mc_snum = snum--;
                cdst->mc_top = snum;
                mdb_cursor_copy(cdst, &mn);
                mn.mc_ki[snum] = 0;
                rc = mdb_update_key(&mn, &bkey);
                if (rc)
                        return rc;
        }

        DPRINTF("moving %s node %u [%s] on page %zu to node %u on page %zu",
            IS_LEAF(csrc->mc_pg[csrc->mc_top]) ? "leaf" : "branch",
            csrc->mc_ki[csrc->mc_top],
                DKEY(&key),
            csrc->mc_pg[csrc->mc_top]->mp_pgno,
            cdst->mc_ki[cdst->mc_top], cdst->mc_pg[cdst->mc_top]->mp_pgno);

        /* Add the node to the destination page.
         */
        rc = mdb_node_add(cdst, cdst->mc_ki[cdst->mc_top], &key, &data, srcpg, flags);
        if (rc != MDB_SUCCESS)
                return rc;

        /* Delete the node from the source page.
         */
        mdb_node_del(csrc->mc_pg[csrc->mc_top], csrc->mc_ki[csrc->mc_top], key.mv_size);

        {
                /* Adjust other cursors pointing to mp */
                MDB_cursor *m2, *m3;
                MDB_dbi dbi = csrc->mc_dbi;
                MDB_page *mp = csrc->mc_pg[csrc->mc_top];

                if (csrc->mc_flags & C_SUB)
                        dbi--;

                for (m2 = csrc->mc_txn->mt_cursors[dbi]; m2; m2=m2->mc_next) {
                        if (csrc->mc_flags & C_SUB)
                                m3 = &m2->mc_xcursor->mx_cursor;
                        else
                                m3 = m2;
                        if (m3 == csrc) continue;
                        if (m3->mc_pg[csrc->mc_top] == mp && m3->mc_ki[csrc->mc_top] ==
                                csrc->mc_ki[csrc->mc_top]) {
                                m3->mc_pg[csrc->mc_top] = cdst->mc_pg[cdst->mc_top];
                                m3->mc_ki[csrc->mc_top] = cdst->mc_ki[cdst->mc_top];
                        }
                }
        }

        /* Update the parent separators.
         */
        if (csrc->mc_ki[csrc->mc_top] == 0) {
                if (csrc->mc_ki[csrc->mc_top-1] != 0) {
                        if (IS_LEAF2(csrc->mc_pg[csrc->mc_top])) {
                                key.mv_data = LEAF2KEY(csrc->mc_pg[csrc->mc_top], 0, key.mv_size);
                        } else {
                                srcnode = NODEPTR(csrc->mc_pg[csrc->mc_top], 0);
                                key.mv_size = NODEKSZ(srcnode);
                                key.mv_data = NODEKEY(srcnode);
                        }
                        DPRINTF("update separator for source page %zu to [%s]",
                                csrc->mc_pg[csrc->mc_top]->mp_pgno, DKEY(&key));
                        mdb_cursor_copy(csrc, &mn);
                        mn.mc_snum--;
                        mn.mc_top--;
                        if ((rc = mdb_update_key(&mn, &key)) != MDB_SUCCESS)
                                return rc;
                }
                if (IS_BRANCH(csrc->mc_pg[csrc->mc_top])) {
                        MDB_val  nullkey;
                        indx_t  ix = csrc->mc_ki[csrc->mc_top];
                        nullkey.mv_size = 0;
                        csrc->mc_ki[csrc->mc_top] = 0;
                        rc = mdb_update_key(csrc, &nullkey);
                        csrc->mc_ki[csrc->mc_top] = ix;
                        assert(rc == MDB_SUCCESS);
                }
        }

        if (cdst->mc_ki[cdst->mc_top] == 0) {
                if (cdst->mc_ki[cdst->mc_top-1] != 0) {
                        if (IS_LEAF2(csrc->mc_pg[csrc->mc_top])) {
                                key.mv_data = LEAF2KEY(cdst->mc_pg[cdst->mc_top], 0, key.mv_size);
                        } else {
                                srcnode = NODEPTR(cdst->mc_pg[cdst->mc_top], 0);
                                key.mv_size = NODEKSZ(srcnode);
                                key.mv_data = NODEKEY(srcnode);
                        }
                        DPRINTF("update separator for destination page %zu to [%s]",
                                cdst->mc_pg[cdst->mc_top]->mp_pgno, DKEY(&key));
                        mdb_cursor_copy(cdst, &mn);
                        mn.mc_snum--;
                        mn.mc_top--;
                        if ((rc = mdb_update_key(&mn, &key)) != MDB_SUCCESS)
                                return rc;
                }
                if (IS_BRANCH(cdst->mc_pg[cdst->mc_top])) {
                        MDB_val  nullkey;
                        indx_t  ix = cdst->mc_ki[cdst->mc_top];
                        nullkey.mv_size = 0;
                        cdst->mc_ki[cdst->mc_top] = 0;
                        rc = mdb_update_key(cdst, &nullkey);
                        cdst->mc_ki[cdst->mc_top] = ix;
                        assert(rc == MDB_SUCCESS);
                }
        }

        return MDB_SUCCESS;
}

/** Merge one page into another.
 *  The nodes from the page pointed to by \b csrc will
 *      be copied to the page pointed to by \b cdst and then
 *      the \b csrc page will be freed.
 * @param[in] csrc Cursor pointing to the source page.
 * @param[in] cdst Cursor pointing to the destination page.
 */
static int
mdb_page_merge(MDB_cursor *csrc, MDB_cursor *cdst)
{
        int                      rc;
        indx_t                   i, j;
        MDB_node                *srcnode;
        MDB_val          key, data;
        unsigned        nkeys;

        DPRINTF("merging page %zu into %zu", csrc->mc_pg[csrc->mc_top]->mp_pgno,
                cdst->mc_pg[cdst->mc_top]->mp_pgno);

        assert(csrc->mc_snum > 1);      /* can't merge root page */
        assert(cdst->mc_snum > 1);

        /* Mark dst as dirty. */
        if ((rc = mdb_page_touch(cdst)))
                return rc;

        /* Move all nodes from src to dst.
         */
        j = nkeys = NUMKEYS(cdst->mc_pg[cdst->mc_top]);
        if (IS_LEAF2(csrc->mc_pg[csrc->mc_top])) {
                key.mv_size = csrc->mc_db->md_pad;
                key.mv_data = METADATA(csrc->mc_pg[csrc->mc_top]);
                for (i = 0; i < NUMKEYS(csrc->mc_pg[csrc->mc_top]); i++, j++) {
                        rc = mdb_node_add(cdst, j, &key, NULL, 0, 0);
                        if (rc != MDB_SUCCESS)
                                return rc;
                        key.mv_data = (char *)key.mv_data + key.mv_size;
                }
        } else {
                for (i = 0; i < NUMKEYS(csrc->mc_pg[csrc->mc_top]); i++, j++) {
                        srcnode = NODEPTR(csrc->mc_pg[csrc->mc_top], i);
                        if (i == 0 && IS_BRANCH(csrc->mc_pg[csrc->mc_top])) {
                                unsigned int snum = csrc->mc_snum;
                                MDB_node *s2;
                                /* must find the lowest key below src */
                                mdb_page_search_lowest(csrc);
                                if (IS_LEAF2(csrc->mc_pg[csrc->mc_top])) {
                                        key.mv_size = csrc->mc_db->md_pad;
                                        key.mv_data = LEAF2KEY(csrc->mc_pg[csrc->mc_top], 0, key.mv_size);
                                } else {
                                        s2 = NODEPTR(csrc->mc_pg[csrc->mc_top], 0);
                                        key.mv_size = NODEKSZ(s2);
                                        key.mv_data = NODEKEY(s2);
                                }
                                csrc->mc_snum = snum--;
                                csrc->mc_top = snum;
                        } else {
                                key.mv_size = srcnode->mn_ksize;
                                key.mv_data = NODEKEY(srcnode);
                        }

                        data.mv_size = NODEDSZ(srcnode);
                        data.mv_data = NODEDATA(srcnode);
                        rc = mdb_node_add(cdst, j, &key, &data, NODEPGNO(srcnode), srcnode->mn_flags);
                        if (rc != MDB_SUCCESS)
                                return rc;
                }
        }

        DPRINTF("dst page %zu now has %u keys (%.1f%% filled)",
            cdst->mc_pg[cdst->mc_top]->mp_pgno, NUMKEYS(cdst->mc_pg[cdst->mc_top]), (float)PAGEFILL(cdst->mc_txn->mt_env, cdst->mc_pg[cdst->mc_top]) / 10);

        /* Unlink the src page from parent and add to free list.
         */
        mdb_node_del(csrc->mc_pg[csrc->mc_top-1], csrc->mc_ki[csrc->mc_top-1], 0);
        if (csrc->mc_ki[csrc->mc_top-1] == 0) {
                key.mv_size = 0;
                csrc->mc_top--;
                rc = mdb_update_key(csrc, &key);
                csrc->mc_top++;
                if (rc)
                        return rc;
        }

        rc = mdb_midl_append(&csrc->mc_txn->mt_free_pgs,
                csrc->mc_pg[csrc->mc_top]->mp_pgno);
        if (rc)
                return rc;
        if (IS_LEAF(csrc->mc_pg[csrc->mc_top]))
                csrc->mc_db->md_leaf_pages--;
        else
                csrc->mc_db->md_branch_pages--;
        {
                /* Adjust other cursors pointing to mp */
                MDB_cursor *m2, *m3;
                MDB_dbi dbi = csrc->mc_dbi;
                MDB_page *mp = cdst->mc_pg[cdst->mc_top];

                if (csrc->mc_flags & C_SUB)
                        dbi--;

                for (m2 = csrc->mc_txn->mt_cursors[dbi]; m2; m2=m2->mc_next) {
                        if (csrc->mc_flags & C_SUB)
                                m3 = &m2->mc_xcursor->mx_cursor;
                        else
                                m3 = m2;
                        if (m3 == csrc) continue;
                        if (m3->mc_snum < csrc->mc_snum) continue;
                        if (m3->mc_pg[csrc->mc_top] == csrc->mc_pg[csrc->mc_top]) {
                                m3->mc_pg[csrc->mc_top] = mp;
                                m3->mc_ki[csrc->mc_top] += nkeys;
                        }
                }
        }
        mdb_cursor_pop(csrc);

        return mdb_rebalance(csrc);
}

/** Copy the contents of a cursor.
 * @param[in] csrc The cursor to copy from.
 * @param[out] cdst The cursor to copy to.
 */
static void
mdb_cursor_copy(const MDB_cursor *csrc, MDB_cursor *cdst)
{
        unsigned int i;

        cdst->mc_txn = csrc->mc_txn;
        cdst->mc_dbi = csrc->mc_dbi;
        cdst->mc_db  = csrc->mc_db;
        cdst->mc_dbx = csrc->mc_dbx;
        cdst->mc_snum = csrc->mc_snum;
        cdst->mc_top = csrc->mc_top;
        cdst->mc_flags = csrc->mc_flags;

        for (i=0; i<csrc->mc_snum; i++) {
                cdst->mc_pg[i] = csrc->mc_pg[i];
                cdst->mc_ki[i] = csrc->mc_ki[i];
        }
}

/** Rebalance the tree after a delete operation.
 * @param[in] mc Cursor pointing to the page where rebalancing
 * should begin.
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_rebalance(MDB_cursor *mc)
{
        MDB_node        *node;
        int rc;
        unsigned int ptop, minkeys;
        MDB_cursor      mn;

        minkeys = 1 + (IS_BRANCH(mc->mc_pg[mc->mc_top]));
#if MDB_DEBUG
        {
        pgno_t pgno;
        COPY_PGNO(pgno, mc->mc_pg[mc->mc_top]->mp_pgno);
        DPRINTF("rebalancing %s page %zu (has %u keys, %.1f%% full)",
            IS_LEAF(mc->mc_pg[mc->mc_top]) ? "leaf" : "branch",
            pgno, NUMKEYS(mc->mc_pg[mc->mc_top]), (float)PAGEFILL(mc->mc_txn->mt_env, mc->mc_pg[mc->mc_top]) / 10);
        }
#endif

        if (PAGEFILL(mc->mc_txn->mt_env, mc->mc_pg[mc->mc_top]) >= FILL_THRESHOLD &&
                NUMKEYS(mc->mc_pg[mc->mc_top]) >= minkeys) {
#if MDB_DEBUG
                pgno_t pgno;
                COPY_PGNO(pgno, mc->mc_pg[mc->mc_top]->mp_pgno);
                DPRINTF("no need to rebalance page %zu, above fill threshold",
                    pgno);
#endif
                return MDB_SUCCESS;
        }

        if (mc->mc_snum < 2) {
                MDB_page *mp = mc->mc_pg[0];
                if (IS_SUBP(mp)) {
                        DPUTS("Can't rebalance a subpage, ignoring");
                        return MDB_SUCCESS;
                }
                if (NUMKEYS(mp) == 0) {
                        DPUTS("tree is completely empty");
                        mc->mc_db->md_root = P_INVALID;
                        mc->mc_db->md_depth = 0;
                        mc->mc_db->md_leaf_pages = 0;
                        rc = mdb_midl_append(&mc->mc_txn->mt_free_pgs, mp->mp_pgno);
                        if (rc)
                                return rc;
                        /* Adjust cursors pointing to mp */
                        mc->mc_snum = 0;
                        mc->mc_top = 0;
                        {
                                MDB_cursor *m2, *m3;
                                MDB_dbi dbi = mc->mc_dbi;

                                if (mc->mc_flags & C_SUB)
                                        dbi--;

                                for (m2 = mc->mc_txn->mt_cursors[dbi]; m2; m2=m2->mc_next) {
                                        if (mc->mc_flags & C_SUB)
                                                m3 = &m2->mc_xcursor->mx_cursor;
                                        else
                                                m3 = m2;
                                        if (m3->mc_snum < mc->mc_snum) continue;
                                        if (m3->mc_pg[0] == mp) {
                                                m3->mc_snum = 0;
                                                m3->mc_top = 0;
                                        }
                                }
                        }
                } else if (IS_BRANCH(mp) && NUMKEYS(mp) == 1) {
                        DPUTS("collapsing root page!");
                        rc = mdb_midl_append(&mc->mc_txn->mt_free_pgs, mp->mp_pgno);
                        if (rc)
                                return rc;
                        mc->mc_db->md_root = NODEPGNO(NODEPTR(mp, 0));
                        rc = mdb_page_get(mc->mc_txn,mc->mc_db->md_root,&mc->mc_pg[0],NULL);
                        if (rc)
                                return rc;
                        mc->mc_db->md_depth--;
                        mc->mc_db->md_branch_pages--;
                        mc->mc_ki[0] = mc->mc_ki[1];
                        {
                                /* Adjust other cursors pointing to mp */
                                MDB_cursor *m2, *m3;
                                MDB_dbi dbi = mc->mc_dbi;

                                if (mc->mc_flags & C_SUB)
                                        dbi--;

                                for (m2 = mc->mc_txn->mt_cursors[dbi]; m2; m2=m2->mc_next) {
                                        if (mc->mc_flags & C_SUB)
                                                m3 = &m2->mc_xcursor->mx_cursor;
                                        else
                                                m3 = m2;
                                        if (m3 == mc || m3->mc_snum < mc->mc_snum) continue;
                                        if (m3->mc_pg[0] == mp) {
                                                m3->mc_pg[0] = mc->mc_pg[0];
                                                m3->mc_snum = 1;
                                                m3->mc_top = 0;
                                                m3->mc_ki[0] = m3->mc_ki[1];
                                        }
                                }
                        }
                } else
                        DPUTS("root page doesn't need rebalancing");
                return MDB_SUCCESS;
        }

        /* The parent (branch page) must have at least 2 pointers,
         * otherwise the tree is invalid.
         */
        ptop = mc->mc_top-1;
        assert(NUMKEYS(mc->mc_pg[ptop]) > 1);

        /* Leaf page fill factor is below the threshold.
         * Try to move keys from left or right neighbor, or
         * merge with a neighbor page.
         */

        /* Find neighbors.
         */
        mdb_cursor_copy(mc, &mn);
        mn.mc_xcursor = NULL;

        if (mc->mc_ki[ptop] == 0) {
                /* We're the leftmost leaf in our parent.
                 */
                DPUTS("reading right neighbor");
                mn.mc_ki[ptop]++;
                node = NODEPTR(mc->mc_pg[ptop], mn.mc_ki[ptop]);
                rc = mdb_page_get(mc->mc_txn,NODEPGNO(node),&mn.mc_pg[mn.mc_top],NULL);
                if (rc)
                        return rc;
                mn.mc_ki[mn.mc_top] = 0;
                mc->mc_ki[mc->mc_top] = NUMKEYS(mc->mc_pg[mc->mc_top]);
        } else {
                /* There is at least one neighbor to the left.
                 */
                DPUTS("reading left neighbor");
                mn.mc_ki[ptop]--;
                node = NODEPTR(mc->mc_pg[ptop], mn.mc_ki[ptop]);
                rc = mdb_page_get(mc->mc_txn,NODEPGNO(node),&mn.mc_pg[mn.mc_top],NULL);
                if (rc)
                        return rc;
                mn.mc_ki[mn.mc_top] = NUMKEYS(mn.mc_pg[mn.mc_top]) - 1;
                mc->mc_ki[mc->mc_top] = 0;
        }

        DPRINTF("found neighbor page %zu (%u keys, %.1f%% full)",
            mn.mc_pg[mn.mc_top]->mp_pgno, NUMKEYS(mn.mc_pg[mn.mc_top]), (float)PAGEFILL(mc->mc_txn->mt_env, mn.mc_pg[mn.mc_top]) / 10);

        /* If the neighbor page is above threshold and has enough keys,
         * move one key from it. Otherwise we should try to merge them.
         * (A branch page must never have less than 2 keys.)
         */
        minkeys = 1 + (IS_BRANCH(mn.mc_pg[mn.mc_top]));
        if (PAGEFILL(mc->mc_txn->mt_env, mn.mc_pg[mn.mc_top]) >= FILL_THRESHOLD && NUMKEYS(mn.mc_pg[mn.mc_top]) > minkeys)
                return mdb_node_move(&mn, mc);
        else {
                if (mc->mc_ki[ptop] == 0)
                        rc = mdb_page_merge(&mn, mc);
                else
                        rc = mdb_page_merge(mc, &mn);
                mc->mc_flags &= ~(C_INITIALIZED|C_EOF);
        }
        return rc;
}

/** Complete a delete operation started by #mdb_cursor_del(). */
static int
mdb_cursor_del0(MDB_cursor *mc, MDB_node *leaf)
{
        int rc;
        MDB_page *mp;
        indx_t ki;

        mp = mc->mc_pg[mc->mc_top];
        ki = mc->mc_ki[mc->mc_top];

        /* add overflow pages to free list */
        if (!IS_LEAF2(mp) && F_ISSET(leaf->mn_flags, F_BIGDATA)) {
                MDB_page *omp;
                pgno_t pg;

                memcpy(&pg, NODEDATA(leaf), sizeof(pg));
                if ((rc = mdb_page_get(mc->mc_txn, pg, &omp, NULL)) ||
                        (rc = mdb_ovpage_free(mc, omp)))
                        return rc;
        }
        mdb_node_del(mp, ki, mc->mc_db->md_pad);
        mc->mc_db->md_entries--;
        rc = mdb_rebalance(mc);
        if (rc != MDB_SUCCESS)
                mc->mc_txn->mt_flags |= MDB_TXN_ERROR;
        /* if mc points past last node in page, invalidate */
        else if (mc->mc_ki[mc->mc_top] >= NUMKEYS(mc->mc_pg[mc->mc_top]))
                mc->mc_flags &= ~(C_INITIALIZED|C_EOF);

        {
                /* Adjust other cursors pointing to mp */
                MDB_cursor *m2;
                unsigned int nkeys;
                MDB_dbi dbi = mc->mc_dbi;

                mp = mc->mc_pg[mc->mc_top];
                nkeys = NUMKEYS(mp);
                for (m2 = mc->mc_txn->mt_cursors[dbi]; m2; m2=m2->mc_next) {
                        if (m2 == mc)
                                continue;
                        if (!(m2->mc_flags & C_INITIALIZED))
                                continue;
                        if (m2->mc_pg[mc->mc_top] == mp) {
                                if (m2->mc_ki[mc->mc_top] > ki)
                                        m2->mc_ki[mc->mc_top]--;
                                if (m2->mc_ki[mc->mc_top] >= nkeys)
                                        m2->mc_flags &= ~(C_INITIALIZED|C_EOF);
                        }
                }
        }

        return rc;
}

int
mdb_del(MDB_txn *txn, MDB_dbi dbi,
    MDB_val *key, MDB_val *data)
{
        MDB_cursor mc;
        MDB_xcursor mx;
        MDB_cursor_op op;
        MDB_val rdata, *xdata;
        int              rc, exact;
        DKBUF;

        assert(key != NULL);

        DPRINTF("====> delete db %u key [%s]", dbi, DKEY(key));

        if (txn == NULL || !dbi || dbi >= txn->mt_numdbs || !(txn->mt_dbflags[dbi] & DB_VALID))
                return EINVAL;

        if (F_ISSET(txn->mt_flags, MDB_TXN_RDONLY)) {
                return EACCES;
        }

        if (key->mv_size == 0 || key->mv_size > MDB_MAXKEYSIZE) {
                return EINVAL;
        }

        mdb_cursor_init(&mc, txn, dbi, &mx);

        exact = 0;
        if (data) {
                op = MDB_GET_BOTH;
                rdata = *data;
                xdata = &rdata;
        } else {
                op = MDB_SET;
                xdata = NULL;
        }
        rc = mdb_cursor_set(&mc, key, xdata, op, &exact);
        if (rc == 0) {
                /* let mdb_page_split know about this cursor if needed:
                 * delete will trigger a rebalance; if it needs to move
                 * a node from one page to another, it will have to
                 * update the parent's separator key(s). If the new sepkey
                 * is larger than the current one, the parent page may
                 * run out of space, triggering a split. We need this
                 * cursor to be consistent until the end of the rebalance.
                 */
                mc.mc_flags |= C_UNTRACK;
                mc.mc_next = txn->mt_cursors[dbi];
                txn->mt_cursors[dbi] = &mc;
                rc = mdb_cursor_del(&mc, data ? 0 : MDB_NODUPDATA);
                txn->mt_cursors[dbi] = mc.mc_next;
        }
        return rc;
}

/** Split a page and insert a new node.
 * @param[in,out] mc Cursor pointing to the page and desired insertion index.
 * The cursor will be updated to point to the actual page and index where
 * the node got inserted after the split.
 * @param[in] newkey The key for the newly inserted node.
 * @param[in] newdata The data for the newly inserted node.
 * @param[in] newpgno The page number, if the new node is a branch node.
 * @param[in] nflags The #NODE_ADD_FLAGS for the new node.
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_page_split(MDB_cursor *mc, MDB_val *newkey, MDB_val *newdata, pgno_t newpgno,
        unsigned int nflags)
{
        unsigned int flags;
        int              rc = MDB_SUCCESS, ins_new = 0, new_root = 0, newpos = 1, did_split = 0;
        indx_t           newindx;
        pgno_t           pgno = 0;
        unsigned int     i, j, split_indx, nkeys, pmax;
        MDB_node        *node;
        MDB_val  sepkey, rkey, xdata, *rdata = &xdata;
        MDB_page        *copy;
        MDB_page        *mp, *rp, *pp;
        unsigned int ptop;
        MDB_cursor      mn;
        DKBUF;

        mp = mc->mc_pg[mc->mc_top];
        newindx = mc->mc_ki[mc->mc_top];

        DPRINTF("-----> splitting %s page %zu and adding [%s] at index %i",
            IS_LEAF(mp) ? "leaf" : "branch", mp->mp_pgno,
            DKEY(newkey), mc->mc_ki[mc->mc_top]);

        /* Create a right sibling. */
        if ((rc = mdb_page_new(mc, mp->mp_flags, 1, &rp)))
                return rc;
        DPRINTF("new right sibling: page %zu", rp->mp_pgno);

        if (mc->mc_snum < 2) {
                if ((rc = mdb_page_new(mc, P_BRANCH, 1, &pp)))
                        return rc;
                /* shift current top to make room for new parent */
                mc->mc_pg[1] = mc->mc_pg[0];
                mc->mc_ki[1] = mc->mc_ki[0];
                mc->mc_pg[0] = pp;
                mc->mc_ki[0] = 0;
                mc->mc_db->md_root = pp->mp_pgno;
                DPRINTF("root split! new root = %zu", pp->mp_pgno);
                mc->mc_db->md_depth++;
                new_root = 1;

                /* Add left (implicit) pointer. */
                if ((rc = mdb_node_add(mc, 0, NULL, NULL, mp->mp_pgno, 0)) != MDB_SUCCESS) {
                        /* undo the pre-push */
                        mc->mc_pg[0] = mc->mc_pg[1];
                        mc->mc_ki[0] = mc->mc_ki[1];
                        mc->mc_db->md_root = mp->mp_pgno;
                        mc->mc_db->md_depth--;
                        return rc;
                }
                mc->mc_snum = 2;
                mc->mc_top = 1;
                ptop = 0;
        } else {
                ptop = mc->mc_top-1;
                DPRINTF("parent branch page is %zu", mc->mc_pg[ptop]->mp_pgno);
        }

        mc->mc_flags |= C_SPLITTING;
        mdb_cursor_copy(mc, &mn);
        mn.mc_pg[mn.mc_top] = rp;
        mn.mc_ki[ptop] = mc->mc_ki[ptop]+1;

        if (nflags & MDB_APPEND) {
                mn.mc_ki[mn.mc_top] = 0;
                sepkey = *newkey;
                split_indx = newindx;
                nkeys = 0;
                goto newsep;
        }

        nkeys = NUMKEYS(mp);
        split_indx = nkeys / 2;
        if (newindx < split_indx)
                newpos = 0;

        if (IS_LEAF2(rp)) {
                char *split, *ins;
                int x;
                unsigned int lsize, rsize, ksize;
                /* Move half of the keys to the right sibling */
                copy = NULL;
                x = mc->mc_ki[mc->mc_top] - split_indx;
                ksize = mc->mc_db->md_pad;
                split = LEAF2KEY(mp, split_indx, ksize);
                rsize = (nkeys - split_indx) * ksize;
                lsize = (nkeys - split_indx) * sizeof(indx_t);
                mp->mp_lower -= lsize;
                rp->mp_lower += lsize;
                mp->mp_upper += rsize - lsize;
                rp->mp_upper -= rsize - lsize;
                sepkey.mv_size = ksize;
                if (newindx == split_indx) {
                        sepkey.mv_data = newkey->mv_data;
                } else {
                        sepkey.mv_data = split;
                }
                if (x<0) {
                        ins = LEAF2KEY(mp, mc->mc_ki[mc->mc_top], ksize);
                        memcpy(rp->mp_ptrs, split, rsize);
                        sepkey.mv_data = rp->mp_ptrs;
                        memmove(ins+ksize, ins, (split_indx - mc->mc_ki[mc->mc_top]) * ksize);
                        memcpy(ins, newkey->mv_data, ksize);
                        mp->mp_lower += sizeof(indx_t);
                        mp->mp_upper -= ksize - sizeof(indx_t);
                } else {
                        if (x)
                                memcpy(rp->mp_ptrs, split, x * ksize);
                        ins = LEAF2KEY(rp, x, ksize);
                        memcpy(ins, newkey->mv_data, ksize);
                        memcpy(ins+ksize, split + x * ksize, rsize - x * ksize);
                        rp->mp_lower += sizeof(indx_t);
                        rp->mp_upper -= ksize - sizeof(indx_t);
                        mc->mc_ki[mc->mc_top] = x;
                        mc->mc_pg[mc->mc_top] = rp;
                }
                goto newsep;
        }

        /* For leaf pages, check the split point based on what
         * fits where, since otherwise mdb_node_add can fail.
         *
         * This check is only needed when the data items are
         * relatively large, such that being off by one will
         * make the difference between success or failure.
         *
         * It's also relevant if a page happens to be laid out
         * such that one half of its nodes are all "small" and
         * the other half of its nodes are "large." If the new
         * item is also "large" and falls on the half with
         * "large" nodes, it also may not fit.
         */
        if (IS_LEAF(mp)) {
                unsigned int psize, nsize;
                /* Maximum free space in an empty page */
                pmax = mc->mc_txn->mt_env->me_psize - PAGEHDRSZ;
                nsize = mdb_leaf_size(mc->mc_txn->mt_env, newkey, newdata);
                if ((nkeys < 20) || (nsize > pmax/16)) {
                        if (newindx <= split_indx) {
                                psize = nsize;
                                newpos = 0;
                                for (i=0; i<split_indx; i++) {
                                        node = NODEPTR(mp, i);
                                        psize += NODESIZE + NODEKSZ(node) + sizeof(indx_t);
                                        if (F_ISSET(node->mn_flags, F_BIGDATA))
                                                psize += sizeof(pgno_t);
                                        else
                                                psize += NODEDSZ(node);
                                        psize += psize & 1;
                                        if (psize > pmax) {
                                                if (i <= newindx) {
                                                        split_indx = newindx;
                                                        if (i < newindx)
                                                                newpos = 1;
                                                }
                                                else
                                                        split_indx = i;
                                                break;
                                        }
                                }
                        } else {
                                psize = nsize;
                                for (i=nkeys-1; i>=split_indx; i--) {
                                        node = NODEPTR(mp, i);
                                        psize += NODESIZE + NODEKSZ(node) + sizeof(indx_t);
                                        if (F_ISSET(node->mn_flags, F_BIGDATA))
                                                psize += sizeof(pgno_t);
                                        else
                                                psize += NODEDSZ(node);
                                        psize += psize & 1;
                                        if (psize > pmax) {
                                                if (i >= newindx) {
                                                        split_indx = newindx;
                                                        newpos = 0;
                                                } else
                                                        split_indx = i+1;
                                                break;
                                        }
                                }
                        }
                }
        }

        /* First find the separating key between the split pages.
         * The case where newindx == split_indx is ambiguous; the
         * new item could go to the new page or stay on the original
         * page. If newpos == 1 it goes to the new page.
         */
        if (newindx == split_indx && newpos) {
                sepkey.mv_size = newkey->mv_size;
                sepkey.mv_data = newkey->mv_data;
        } else {
                node = NODEPTR(mp, split_indx);
                sepkey.mv_size = node->mn_ksize;
                sepkey.mv_data = NODEKEY(node);
        }

newsep:
        DPRINTF("separator is [%s]", DKEY(&sepkey));

        /* Copy separator key to the parent.
         */
        if (SIZELEFT(mn.mc_pg[ptop]) < mdb_branch_size(mc->mc_txn->mt_env, &sepkey)) {
                mn.mc_snum--;
                mn.mc_top--;
                did_split = 1;
                rc = mdb_page_split(&mn, &sepkey, NULL, rp->mp_pgno, 0);

                /* root split? */
                if (mn.mc_snum == mc->mc_snum) {
                        mc->mc_pg[mc->mc_snum] = mc->mc_pg[mc->mc_top];
                        mc->mc_ki[mc->mc_snum] = mc->mc_ki[mc->mc_top];
                        mc->mc_pg[mc->mc_top] = mc->mc_pg[ptop];
                        mc->mc_ki[mc->mc_top] = mc->mc_ki[ptop];
                        mc->mc_snum++;
                        mc->mc_top++;
                        ptop++;
                }
                /* Right page might now have changed parent.
                 * Check if left page also changed parent.
                 */
                if (mn.mc_pg[ptop] != mc->mc_pg[ptop] &&
                    mc->mc_ki[ptop] >= NUMKEYS(mc->mc_pg[ptop])) {
                        for (i=0; i<ptop; i++) {
                                mc->mc_pg[i] = mn.mc_pg[i];
                                mc->mc_ki[i] = mn.mc_ki[i];
                        }
                        mc->mc_pg[ptop] = mn.mc_pg[ptop];
                        mc->mc_ki[ptop] = mn.mc_ki[ptop] - 1;
                }
        } else {
                mn.mc_top--;
                rc = mdb_node_add(&mn, mn.mc_ki[ptop], &sepkey, NULL, rp->mp_pgno, 0);
                mn.mc_top++;
        }
        mc->mc_flags ^= C_SPLITTING;
        if (rc != MDB_SUCCESS) {
                return rc;
        }
        if (nflags & MDB_APPEND) {
                mc->mc_pg[mc->mc_top] = rp;
                mc->mc_ki[mc->mc_top] = 0;
                rc = mdb_node_add(mc, 0, newkey, newdata, newpgno, nflags);
                if (rc)
                        return rc;
                for (i=0; i<mc->mc_top; i++)
                        mc->mc_ki[i] = mn.mc_ki[i];
                goto done;
        }
        if (IS_LEAF2(rp)) {
                goto done;
        }

        /* Move half of the keys to the right sibling. */

        /* grab a page to hold a temporary copy */
        copy = mdb_page_malloc(mc->mc_txn, 1);
        if (copy == NULL)
                return ENOMEM;

        copy->mp_pgno  = mp->mp_pgno;
        copy->mp_flags = mp->mp_flags;
        copy->mp_lower = PAGEHDRSZ;
        copy->mp_upper = mc->mc_txn->mt_env->me_psize;
        mc->mc_pg[mc->mc_top] = copy;
        for (i = j = 0; i <= nkeys; j++) {
                if (i == split_indx) {
                /* Insert in right sibling. */
                /* Reset insert index for right sibling. */
                        if (i != newindx || (newpos ^ ins_new)) {
                                j = 0;
                                mc->mc_pg[mc->mc_top] = rp;
                        }
                }

                if (i == newindx && !ins_new) {
                        /* Insert the original entry that caused the split. */
                        rkey.mv_data = newkey->mv_data;
                        rkey.mv_size = newkey->mv_size;
                        if (IS_LEAF(mp)) {
                                rdata = newdata;
                        } else
                                pgno = newpgno;
                        flags = nflags;

                        ins_new = 1;

                        /* Update index for the new key. */
                        mc->mc_ki[mc->mc_top] = j;
                } else if (i == nkeys) {
                        break;
                } else {
                        node = NODEPTR(mp, i);
                        rkey.mv_data = NODEKEY(node);
                        rkey.mv_size = node->mn_ksize;
                        if (IS_LEAF(mp)) {
                                xdata.mv_data = NODEDATA(node);
                                xdata.mv_size = NODEDSZ(node);
                                rdata = &xdata;
                        } else
                                pgno = NODEPGNO(node);
                        flags = node->mn_flags;

                        i++;
                }

                if (!IS_LEAF(mp) && j == 0) {
                        /* First branch index doesn't need key data. */
                        rkey.mv_size = 0;
                }

                rc = mdb_node_add(mc, j, &rkey, rdata, pgno, flags);
                if (rc) break;
        }

        nkeys = NUMKEYS(copy);
        for (i=0; i<nkeys; i++)
                mp->mp_ptrs[i] = copy->mp_ptrs[i];
        mp->mp_lower = copy->mp_lower;
        mp->mp_upper = copy->mp_upper;
        memcpy(NODEPTR(mp, nkeys-1), NODEPTR(copy, nkeys-1),
                mc->mc_txn->mt_env->me_psize - copy->mp_upper);

        /* reset back to original page */
        if (newindx < split_indx || (!newpos && newindx == split_indx)) {
                mc->mc_pg[mc->mc_top] = mp;
                if (nflags & MDB_RESERVE) {
                        node = NODEPTR(mp, mc->mc_ki[mc->mc_top]);
                        if (!(node->mn_flags & F_BIGDATA))
                                newdata->mv_data = NODEDATA(node);
                }
        } else {
                mc->mc_ki[ptop]++;
                /* Make sure mc_ki is still valid.
                 */
                if (mn.mc_pg[ptop] != mc->mc_pg[ptop] &&
                    mc->mc_ki[ptop] >= NUMKEYS(mc->mc_pg[ptop])) {
                        for (i=0; i<ptop; i++) {
                                mc->mc_pg[i] = mn.mc_pg[i];
                                mc->mc_ki[i] = mn.mc_ki[i];
                        }
                        mc->mc_pg[ptop] = mn.mc_pg[ptop];
                        mc->mc_ki[ptop] = mn.mc_ki[ptop] - 1;
                }
        }

        /* return tmp page to freelist */
        mdb_page_free(mc->mc_txn->mt_env, copy);
done:
        {
                /* Adjust other cursors pointing to mp */
                MDB_cursor *m2, *m3;
                MDB_dbi dbi = mc->mc_dbi;
                int fixup = NUMKEYS(mp);

                if (mc->mc_flags & C_SUB)
                        dbi--;

                for (m2 = mc->mc_txn->mt_cursors[dbi]; m2; m2=m2->mc_next) {
                        if (mc->mc_flags & C_SUB)
                                m3 = &m2->mc_xcursor->mx_cursor;
                        else
                                m3 = m2;
                        if (m3 == mc)
                                continue;
                        if (!(m2->mc_flags & m3->mc_flags & C_INITIALIZED))
                                continue;
                        if (m3->mc_flags & C_SPLITTING)
                                continue;
                        if (new_root) {
                                int k;
                                /* root split */
                                for (k=m3->mc_top; k>=0; k--) {
                                        m3->mc_ki[k+1] = m3->mc_ki[k];
                                        m3->mc_pg[k+1] = m3->mc_pg[k];
                                }
                                if (m3->mc_ki[0] >= split_indx) {
                                        m3->mc_ki[0] = 1;
                                } else {
                                        m3->mc_ki[0] = 0;
                                }
                                m3->mc_pg[0] = mc->mc_pg[0];
                                m3->mc_snum++;
                                m3->mc_top++;
                        }
                        if (m3->mc_pg[mc->mc_top] == mp) {
                                if (m3->mc_ki[mc->mc_top] >= newindx && !(nflags & MDB_SPLIT_REPLACE))
                                        m3->mc_ki[mc->mc_top]++;
                                if (m3->mc_ki[mc->mc_top] >= fixup) {
                                        m3->mc_pg[mc->mc_top] = rp;
                                        m3->mc_ki[mc->mc_top] -= fixup;
                                        m3->mc_ki[ptop] = mn.mc_ki[ptop];
                                }
                        } else if (!did_split && m3->mc_pg[ptop] == mc->mc_pg[ptop] &&
                                m3->mc_ki[ptop] >= mc->mc_ki[ptop]) {
                                m3->mc_ki[ptop]++;
                        }
                }
        }
        return rc;
}

int
mdb_put(MDB_txn *txn, MDB_dbi dbi,
    MDB_val *key, MDB_val *data, unsigned int flags)
{
        MDB_cursor mc;
        MDB_xcursor mx;

        assert(key != NULL);
        assert(data != NULL);

        if (txn == NULL || !dbi || dbi >= txn->mt_numdbs || !(txn->mt_dbflags[dbi] & DB_VALID))
                return EINVAL;

        if (F_ISSET(txn->mt_flags, MDB_TXN_RDONLY)) {
                return EACCES;
        }

        if (key->mv_size == 0 || key->mv_size > MDB_MAXKEYSIZE) {
                return EINVAL;
        }

        if ((flags & (MDB_NOOVERWRITE|MDB_NODUPDATA|MDB_RESERVE|MDB_APPEND|MDB_APPENDDUP)) != flags)
                return EINVAL;

        mdb_cursor_init(&mc, txn, dbi, &mx);
        return mdb_cursor_put(&mc, key, data, flags);
}

int
mdb_env_set_flags(MDB_env *env, unsigned int flag, int onoff)
{
        if ((flag & CHANGEABLE) != flag)
                return EINVAL;
        if (onoff)
                env->me_flags |= flag;
        else
                env->me_flags &= ~flag;
        return MDB_SUCCESS;
}

int
mdb_env_get_flags(MDB_env *env, unsigned int *arg)
{
        if (!env || !arg)
                return EINVAL;

        *arg = env->me_flags;
        return MDB_SUCCESS;
}

int
mdb_env_get_path(MDB_env *env, const char **arg)
{
        if (!env || !arg)
                return EINVAL;

        *arg = env->me_path;
        return MDB_SUCCESS;
}

/** Common code for #mdb_stat() and #mdb_env_stat().
 * @param[in] env the environment to operate in.
 * @param[in] db the #MDB_db record containing the stats to return.
 * @param[out] arg the address of an #MDB_stat structure to receive the stats.
 * @return 0, this function always succeeds.
 */
static int
mdb_stat0(MDB_env *env, MDB_db *db, MDB_stat *arg)
{
        arg->ms_psize = env->me_psize;
        arg->ms_depth = db->md_depth;
        arg->ms_branch_pages = db->md_branch_pages;
        arg->ms_leaf_pages = db->md_leaf_pages;
        arg->ms_overflow_pages = db->md_overflow_pages;
        arg->ms_entries = db->md_entries;

        return MDB_SUCCESS;
}
int
mdb_env_stat(MDB_env *env, MDB_stat *arg)
{
        int toggle;

        if (env == NULL || arg == NULL)
                return EINVAL;

        toggle = mdb_env_pick_meta(env);

        return mdb_stat0(env, &env->me_metas[toggle]->mm_dbs[MAIN_DBI], arg);
}

int
mdb_env_info(MDB_env *env, MDB_envinfo *arg)
{
        int toggle;

        if (env == NULL || arg == NULL)
                return EINVAL;

        toggle = mdb_env_pick_meta(env);
        arg->me_mapaddr = (env->me_flags & MDB_FIXEDMAP) ? env->me_map : 0;
        arg->me_mapsize = env->me_mapsize;
        arg->me_maxreaders = env->me_maxreaders;
        arg->me_numreaders = env->me_numreaders;
        arg->me_last_pgno = env->me_metas[toggle]->mm_last_pg;
        arg->me_last_txnid = env->me_metas[toggle]->mm_txnid;
        return MDB_SUCCESS;
}

/** Set the default comparison functions for a database.
 * Called immediately after a database is opened to set the defaults.
 * The user can then override them with #mdb_set_compare() or
 * #mdb_set_dupsort().
 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
 * @param[in] dbi A database handle returned by #mdb_dbi_open()
 */
static void
mdb_default_cmp(MDB_txn *txn, MDB_dbi dbi)
{
        uint16_t f = txn->mt_dbs[dbi].md_flags;

        txn->mt_dbxs[dbi].md_cmp =
                (f & MDB_REVERSEKEY) ? mdb_cmp_memnr :
                (f & MDB_INTEGERKEY) ? mdb_cmp_cint  : mdb_cmp_memn;

        txn->mt_dbxs[dbi].md_dcmp =
                !(f & MDB_DUPSORT) ? 0 :
                ((f & MDB_INTEGERDUP)
                 ? ((f & MDB_DUPFIXED)   ? mdb_cmp_int   : mdb_cmp_cint)
                 : ((f & MDB_REVERSEDUP) ? mdb_cmp_memnr : mdb_cmp_memn));
}

int mdb_dbi_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *dbi)
{
        MDB_val key, data;
        MDB_dbi i;
        MDB_cursor mc;
        int rc, dbflag, exact;
        unsigned int unused = 0;
        size_t len;

        if (txn->mt_dbxs[FREE_DBI].md_cmp == NULL) {
                mdb_default_cmp(txn, FREE_DBI);
        }

        if ((flags & VALID_FLAGS) != flags)
                return EINVAL;

        /* main DB? */
        if (!name) {
                *dbi = MAIN_DBI;
                if (flags & PERSISTENT_FLAGS) {
                        uint16_t f2 = flags & PERSISTENT_FLAGS;
                        /* make sure flag changes get committed */
                        if ((txn->mt_dbs[MAIN_DBI].md_flags | f2) != txn->mt_dbs[MAIN_DBI].md_flags) {
                                txn->mt_dbs[MAIN_DBI].md_flags |= f2;
                                txn->mt_flags |= MDB_TXN_DIRTY;
                        }
                }
                mdb_default_cmp(txn, MAIN_DBI);
                return MDB_SUCCESS;
        }

        if (txn->mt_dbxs[MAIN_DBI].md_cmp == NULL) {
                mdb_default_cmp(txn, MAIN_DBI);
        }

        /* Is the DB already open? */
        len = strlen(name);
        for (i=2; i<txn->mt_numdbs; i++) {
                if (!txn->mt_dbxs[i].md_name.mv_size) {
                        /* Remember this free slot */
                        if (!unused) unused = i;
                        continue;
                }
                if (len == txn->mt_dbxs[i].md_name.mv_size &&
                        !strncmp(name, txn->mt_dbxs[i].md_name.mv_data, len)) {
                        *dbi = i;
                        return MDB_SUCCESS;
                }
        }

        /* If no free slot and max hit, fail */
        if (!unused && txn->mt_numdbs >= txn->mt_env->me_maxdbs)
                return MDB_DBS_FULL;

        /* Cannot mix named databases with some mainDB flags */
        if (txn->mt_dbs[MAIN_DBI].md_flags & (MDB_DUPSORT|MDB_INTEGERKEY))
                return (flags & MDB_CREATE) ? MDB_INCOMPATIBLE : MDB_NOTFOUND;

        /* Find the DB info */
        dbflag = DB_NEW|DB_VALID;
        exact = 0;
        key.mv_size = len;
        key.mv_data = (void *)name;
        mdb_cursor_init(&mc, txn, MAIN_DBI, NULL);
        rc = mdb_cursor_set(&mc, &key, &data, MDB_SET, &exact);
        if (rc == MDB_SUCCESS) {
                /* make sure this is actually a DB */
                MDB_node *node = NODEPTR(mc.mc_pg[mc.mc_top], mc.mc_ki[mc.mc_top]);
                if (!(node->mn_flags & F_SUBDATA))
                        return EINVAL;
        } else if (rc == MDB_NOTFOUND && (flags & MDB_CREATE)) {
                /* Create if requested */
                MDB_db dummy;
                data.mv_size = sizeof(MDB_db);
                data.mv_data = &dummy;
                memset(&dummy, 0, sizeof(dummy));
                dummy.md_root = P_INVALID;
                dummy.md_flags = flags & PERSISTENT_FLAGS;
                rc = mdb_cursor_put(&mc, &key, &data, F_SUBDATA);
                dbflag |= DB_DIRTY;
        }

        /* OK, got info, add to table */
        if (rc == MDB_SUCCESS) {
                unsigned int slot = unused ? unused : txn->mt_numdbs;
                txn->mt_dbxs[slot].md_name.mv_data = strdup(name);
                txn->mt_dbxs[slot].md_name.mv_size = len;
                txn->mt_dbxs[slot].md_rel = NULL;
                txn->mt_dbflags[slot] = dbflag;
                memcpy(&txn->mt_dbs[slot], data.mv_data, sizeof(MDB_db));
                *dbi = slot;
                txn->mt_env->me_dbflags[slot] = txn->mt_dbs[slot].md_flags;
                mdb_default_cmp(txn, slot);
                if (!unused) {
                        txn->mt_numdbs++;
                }
        }

        return rc;
}

int mdb_stat(MDB_txn *txn, MDB_dbi dbi, MDB_stat *arg)
{
        if (txn == NULL || arg == NULL || dbi >= txn->mt_numdbs)
                return EINVAL;

        if (txn->mt_dbflags[dbi] & DB_STALE) {
                MDB_cursor mc;
                MDB_xcursor mx;
                /* Stale, must read the DB's root. cursor_init does it for us. */
                mdb_cursor_init(&mc, txn, dbi, &mx);
        }
        return mdb_stat0(txn->mt_env, &txn->mt_dbs[dbi], arg);
}

void mdb_dbi_close(MDB_env *env, MDB_dbi dbi)
{
        char *ptr;
        if (dbi <= MAIN_DBI || dbi >= env->me_maxdbs)
                return;
        ptr = env->me_dbxs[dbi].md_name.mv_data;
        env->me_dbxs[dbi].md_name.mv_data = NULL;
        env->me_dbxs[dbi].md_name.mv_size = 0;
        env->me_dbflags[dbi] = 0;
        free(ptr);
}

/** Add all the DB's pages to the free list.
 * @param[in] mc Cursor on the DB to free.
 * @param[in] subs non-Zero to check for sub-DBs in this DB.
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_drop0(MDB_cursor *mc, int subs)
{
        int rc;

        rc = mdb_page_search(mc, NULL, 0);
        if (rc == MDB_SUCCESS) {
                MDB_txn *txn = mc->mc_txn;
                MDB_node *ni;
                MDB_cursor mx;
                unsigned int i;

                /* LEAF2 pages have no nodes, cannot have sub-DBs */
                if (IS_LEAF2(mc->mc_pg[mc->mc_top]))
                        mdb_cursor_pop(mc);

                mdb_cursor_copy(mc, &mx);
                while (mc->mc_snum > 0) {
                        MDB_page *mp = mc->mc_pg[mc->mc_top];
                        unsigned n = NUMKEYS(mp);
                        if (IS_LEAF(mp)) {
                                for (i=0; i<n; i++) {
                                        ni = NODEPTR(mp, i);
                                        if (ni->mn_flags & F_BIGDATA) {
                                                MDB_page *omp;
                                                pgno_t pg;
                                                memcpy(&pg, NODEDATA(ni), sizeof(pg));
                                                rc = mdb_page_get(txn, pg, &omp, NULL);
                                                if (rc != 0)
                                                        return rc;
                                                assert(IS_OVERFLOW(omp));
                                                rc = mdb_midl_append_range(&txn->mt_free_pgs,
                                                        pg, omp->mp_pages);
                                                if (rc)
                                                        return rc;
                                        } else if (subs && (ni->mn_flags & F_SUBDATA)) {
                                                mdb_xcursor_init1(mc, ni);
                                                rc = mdb_drop0(&mc->mc_xcursor->mx_cursor, 0);
                                                if (rc)
                                                        return rc;
                                        }
                                }
                        } else {
                                if ((rc = mdb_midl_need(&txn->mt_free_pgs, n)) != 0)
                                        return rc;
                                for (i=0; i<n; i++) {
                                        pgno_t pg;
                                        ni = NODEPTR(mp, i);
                                        pg = NODEPGNO(ni);
                                        /* free it */
                                        mdb_midl_xappend(txn->mt_free_pgs, pg);
                                }
                        }
                        if (!mc->mc_top)
                                break;
                        mc->mc_ki[mc->mc_top] = i;
                        rc = mdb_cursor_sibling(mc, 1);
                        if (rc) {
                                /* no more siblings, go back to beginning
                                 * of previous level.
                                 */
                                mdb_cursor_pop(mc);
                                mc->mc_ki[0] = 0;
                                for (i=1; i<mc->mc_snum; i++) {
                                        mc->mc_ki[i] = 0;
                                        mc->mc_pg[i] = mx.mc_pg[i];
                                }
                        }
                }
                /* free it */
                rc = mdb_midl_append(&txn->mt_free_pgs, mc->mc_db->md_root);
        } else if (rc == MDB_NOTFOUND) {
                rc = MDB_SUCCESS;
        }
        return rc;
}

int mdb_drop(MDB_txn *txn, MDB_dbi dbi, int del)
{
        MDB_cursor *mc, *m2;
        int rc;

        if (!txn || !dbi || dbi >= txn->mt_numdbs || (unsigned)del > 1 || !(txn->mt_dbflags[dbi] & DB_VALID))
                return EINVAL;

        if (F_ISSET(txn->mt_flags, MDB_TXN_RDONLY))
                return EACCES;

        rc = mdb_cursor_open(txn, dbi, &mc);
        if (rc)
                return rc;

        rc = mdb_drop0(mc, mc->mc_db->md_flags & MDB_DUPSORT);
        /* Invalidate the dropped DB's cursors */
        for (m2 = txn->mt_cursors[dbi]; m2; m2 = m2->mc_next)
                m2->mc_flags &= ~(C_INITIALIZED|C_EOF);
        if (rc)
                goto leave;

        /* Can't delete the main DB */
        if (del && dbi > MAIN_DBI) {
                rc = mdb_del(txn, MAIN_DBI, &mc->mc_dbx->md_name, NULL);
                if (!rc) {
                        txn->mt_dbflags[dbi] = DB_STALE;
                        mdb_dbi_close(txn->mt_env, dbi);
                }
        } else {
                /* reset the DB record, mark it dirty */
                txn->mt_dbflags[dbi] |= DB_DIRTY;
                txn->mt_dbs[dbi].md_depth = 0;
                txn->mt_dbs[dbi].md_branch_pages = 0;
                txn->mt_dbs[dbi].md_leaf_pages = 0;
                txn->mt_dbs[dbi].md_overflow_pages = 0;
                txn->mt_dbs[dbi].md_entries = 0;
                txn->mt_dbs[dbi].md_root = P_INVALID;

                txn->mt_flags |= MDB_TXN_DIRTY;
        }
leave:
        mdb_cursor_close(mc);
        return rc;
}

int mdb_set_compare(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp)
{
        if (txn == NULL || !dbi || dbi >= txn->mt_numdbs || !(txn->mt_dbflags[dbi] & DB_VALID))
                return EINVAL;

        txn->mt_dbxs[dbi].md_cmp = cmp;
        return MDB_SUCCESS;
}

int mdb_set_dupsort(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp)
{
        if (txn == NULL || !dbi || dbi >= txn->mt_numdbs || !(txn->mt_dbflags[dbi] & DB_VALID))
                return EINVAL;

        txn->mt_dbxs[dbi].md_dcmp = cmp;
        return MDB_SUCCESS;
}

int mdb_set_relfunc(MDB_txn *txn, MDB_dbi dbi, MDB_rel_func *rel)
{
        if (txn == NULL || !dbi || dbi >= txn->mt_numdbs || !(txn->mt_dbflags[dbi] & DB_VALID))
                return EINVAL;

        txn->mt_dbxs[dbi].md_rel = rel;
        return MDB_SUCCESS;
}

int mdb_set_relctx(MDB_txn *txn, MDB_dbi dbi, void *ctx)
{
        if (txn == NULL || !dbi || dbi >= txn->mt_numdbs || !(txn->mt_dbflags[dbi] & DB_VALID))
                return EINVAL;

        txn->mt_dbxs[dbi].md_relctx = ctx;
        return MDB_SUCCESS;
}

/** @} */